Lexikon

persistence is the capacity of a substance to remain chemically stable. This is an important factor in estimating the environmental effects of substances discharged into the environment. Certain toxic substances (e.g. cyanides) have a low persistence, whereas other less immediately toxic substances (e.g. many organochlorines) have a high persistence and may therefore produce more serious effects.

persistent and very persistent substances are which persist in the environment for a long time. The cause for that is, that the substance is not degradable by light or other radiation, heat, oxygen, water or moisture nor on biological effects. Many of the xenobiotics are designed to be persistent in the environment (similar to drugs in the body), otherwise the amount to be applied and as a consequence the cost of the substance would be very high, while the efficiency , due to too short contact-time and not stable concentration would be limited.

Hazard and persistency together increase the risk of the substance, given as ecosystem or humans are exposed for longer time to the substance, so it has higher chance to effectuate its harm.

According to REACH regulation substance fulfils the persistence criterion when:
– the half-life in marine water is higher than 60 days, or
– the half-life in fresh- or estuarine water is higher than 40 days, or
– the half-life in marine sediment is higher than 180 days, or
– the half-life in fresh- or estuarine water sediment is higher than 120 days, or
– the half-life in soil is higher than 120 days.

Annex XIII of REACH defines criteria for the identification of substances that are Persistent, Bio-accumulative and Toxic (PBTs) and Annex I lays down general provisions for PBT assessment. PBTs are substances of very high concern (SVHC) and may be included in Annex XIV and by that be made subject to authorisation (Source: REACH)

pharmacokinetics or toxicokinetics is "defined as the study of the rates of absorption, distribution, metabolism, and excretion of toxic substances or substances under toxicological study" (OECD). Pharmacokinetics/toxicokinetics testing involves describing "the bioavailability of a substance and its kinetic and metabolic fate within the body". Pharmacokinetics is also the term used to describe the assessment of absorption, distribution and metabolism in the context of drug preclinical testing.

Metabolism has been "defined as all aspects of the fate of a substance in an organism ..." by OECD; however, metabolism generally refers to the biotransformation of a substance (via an enzymatic or nonenzymatic process) within the body to other molecular species (usually called the metabolites). For ingested substances, metabolism primarily takes place in the liver, although many organs and tissues have metabolic capability. Two types of enzymes are involved in metabolism: phase 1 (cytochrome P450 enzyme family) and phase 2 enzymes.

An understanding of the metabolism of a substance in the body is critical to understanding its toxicity. For example, biotransformation sometimes results in a molecular species being generated that is more toxic than the original substance. The lack of metabolism of a substance can result in its bioaccumulation in the body. Understanding a substance's metabolism can also facilitate identification of possible target organs and the route of clearance.

Pharmacokinetic/toxicokinetic data may be used to:

1. assist in the interpretation of other toxicological data,
2. select doses for other toxicological studies, and/or
3. extrapolate data from animals to the human (OECD).

Source: http://alttox.org/ttrc/toxicity-tests/pharmacokinetics-metabolism/

pharmacology is the closest related branch of applied science to human toxicology, which is the study of drug action. The methodology is very similar to human toxicity assessment, the difference is, that drugs are applied for their beneficial effects on human or other organisms, and the main effect has a special target (e.g. to kill pathogens or harmful cells, etc.). More specifically, pharmacology is the study of the interactions that occur between a living organism and the chemicals substance, the drug, that affect biochemical function. If the substances have medicinal properties, they are considered pharmaceuticals and the assessment is pharmacological assessment. If the drug is a toxicant, toxicology is dealing with its effects. As all drugs, even if they have a dose range, which leads to medicinal application, they are toxicants, it also underlines that the methodologies are very closely related, mainly the aim differentiates pharmacology from toxicology.

physical weathering is caused by the effects of changing temperature on rocks, causing the rock to break apart. The process is sometimes assisted by water.

There are two main types of physical weathering:

• Freeze-thaw occurs when water continually seeps into cracks, freezes and expands, eventually breaking the rock apart.
• Exfoliation occurs when minerals in the rocks are continuously heated and cooled in hot climates.
• On the effect of cristal-formation of salts or oxide formation of iron or other metals. Increased volume of these chemical componunds break the rock.
• Plnat root growth is able to break the rock too.

Physical weathering happens especially in places places where there is little soil and few plants grow, such as in mountain regions and hot deserts. Either through repeated melting and freezing of water (mountains and tundra) or through expansion and contraction of the surface layer of rocks that are baked by the sun (hot deserts).

hysico-chemical testing methods for chemical substances: COUNCIL REGULATION (EC) No 440/2008 of 30 May 2008 laying down test methods pursuant to Regulation (EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH).

(1) Pursuant to Regulation (EC) No 1907/2006, test methods are to be adopted at Community level for the purposes of tests on substances where such tests are required to generate information on intrinsic properties of substances.

(2) Council Directive 67/548/EEC of 27 June 1967 on the approximation of the laws, regulations and administrative provisions relating to the classification, packaging and labelling of dangerous substances laid down, in Annex V, methods for the determination of the physico-chemical properties, toxicity and ecotoxicity of substances and preparations. Annex V to Directive 67/548/EEC has been deleted by Directive 2006/121/EC of the European Parliament and of the Council with effect from 1 June 2008.

(3) The test methods contained in Annex V to Directive 67/ 548/EEC should be incorporated into this Regulation.

(4) This Regulation does not exclude the use of other test methods, provided that their use is in accordance with Article 13(3) of Regulation 1907/2006.

(5) The principles of replacement, reduction and refinement of the use of animals in procedures should be fully taken into account in the design of the test methods, in particular when appropriate validated methods become available to replace, reduce or refine animal testing.

(6) The provisions of this Regulation are in accordance with the opinion of the Committee established under Article 133 of Regulation (EC) No 1907/2006

Article 1: The test methods to be applied for the purposes of Regulation 1907/2006/EC are set out in the Annex to this Regulation.

Article 2: The Commission shall review, where appropriate, the test methods contained in this Regulation with a view to replacing, reducing or refining testing on vertebrate animals.

Article 3: All references to Annex V to Directive 67/548/EEC shall be construed as references to this Regulation.

Article 4: This Regulation shall enter into force on the day following its publication in the Official Journal of the European Union.

It shall apply from 1 June 2008.

LIST OF METHODS FOR THE DETERMINATION OF PHYSICO-CHEMICAL PROPERTIES OF CHEMICAL SUBSTANCES

A.1. Melting/freezing temperature
A.2. Boiling temperature
A.3. Relative density
A.4. Vapour pressure
A.5. Surface tension
A.6. Water solubility
A.8. Partition coefficient
A.9. Flash-point
A.10. Flammability (solids)
A.11. Flammability (gases)
A.12. Flammability (contact with water)
A.13. Pyrophoric properties of solids and liquids
A.14. Explosive properties
A.15. Auto-ignition temperature (liquids and gases)
A.16. Relative self-ignition temperature for solids
A.17. Oxidising properties (solids)
A.18. Number – average molecular weight and molecular weight distribution of Polymers
A.19. Low molecular weight content of polymers
A.20. Solution/extraction behaviour of polymers in water
A.21. Oxidising properties (liquids)

phytotechnology is broadly defined as the use of vegetation to address contaminants in soil, sediment, surface water, and groundwater. Cleanup objectives for phytotechnologies can be contaminant removal and destruction, control and containment, or both. Phytoremediation (i.e., contaminant removal and destruction) is a phytotechnology subset (ITRC 2009).

While phytotechnologies generally are applied in situ, ex situ applications (e.g., hydroponics systems) are possible. Typical organic contaminants, such as petroleum hydrocarbons, gas condensates, crude oil, chlorinated compounds, pesticides, and explosive compounds, can be addressed using plant-based methods. Phytotechnologies also can be applied to typical inorganic contaminants, such as heavy metals, metalloids, radioactive materials, and salts (ITRC 2009).

Six major plant mechanisms enable phytotechnologies to remove, destroy, transfer, stabilize, or contain contaminants:

1.Phytoextraction

Phytoextraction involves contaminant uptake by plant roots, with subsequent accumulation in plant tissue. Plants that accumulate contaminants may require periodic harvesting and proper disposal to avoid recontaminating the soil when the plants die or drop their leaves. Phytoextraction typically is used to address inorganic contaminants, such as metals, metalloids, and radionuclides. Organic contaminants are more likely to be transformed rather than accumulated within the plant tissue. Successful field applications of phytoextraction to take up metals have been limited; however, promising research is underway for using phytoextraction on mercury and persistent organic pollutants (USEPA 2006).

Pesticides classified as persistent organic pollutants resist biodegradation and can remain in the environment for decades. Scientists have identified plants that are capable of extracting chemicals, such as chlordane and 2,2-bis(p-chlorophenyl)1,1-dichloroethene (p,p'-DDE), and storing them in their roots, leaves, and fruits (USEPA 2006).

Plants used in phytoextraction (e.g., Indian mustard, Alpine pennycress, sunflowers, ferns, grasses) typically are effective only in the top one foot of soil because of their shallow root systems and generally slow growth. Researchers are working on genetic modifications that increase the survivability of plants that hyperaccumulate toxic contaminants (USEPA 2006).

2. Phytodegradation

Like phytoextraction, phytodegradation involves the uptake of contaminants; however, metabolic processes within the plant subsequently break down the contaminants. Phytodegradation also encompasses the breakdown of contaminants in the soil through the effects of enzymes and other compounds produced by plant tissues other than the roots (USEPA 2006).

Phytodegradation is applicable to organic contaminants. Their uptake is affected by their hydrophobicity, solubility, and polarity; moderately hydrophobic and polar compounds are more likely to be taken up after sorbing to plant roots. Chlorinated solvents, herbicides, insecticides, pentachlorophenol (PCP), polychlorinated biphenyls (PCBs), and munitions constituents have phytodegradation potential (USEPA 2006).

3. Phytovolatilization

Phytovolatilization is the uptake of a contaminant into a plant and its subsequent transpiration to the atmosphere, or the transformation or phytodegradation of the contaminant with subsequent transpiration of the transformation or degradation products to the atmosphere. Phytovolatilization generally is applied to groundwater but also can be applied to soluble soil contaminants (USEPA 2006).

Transformation or degradation of the contaminant within the plant can create a less toxic product that is transpired; however, degradation of some contaminants, like trichloroethene (TCE), may produce even more toxic products (e.g., vinyl chloride). Once in the atmosphere, these products may be degraded more effectively by sunlight (photodegradation) than they would be by the plant (phytodegradation), but the potential advantages and disadvantages of phytovolatilization must be assessed on a site-specific basis (USEPA 2006).

Phytovolatilization has been applied to both organic and inorganic (e.g., selenium, mercury, arsenic) contaminants, but it must be reiterated that simply volatilizing a contaminant may not be an acceptable alternative (USEPA 2006).

4.Rhizodegradation

The rhizosphere is the zone of soil influenced by plant roots. Essentially, rhizodegradation is "plant-assisted bioremediation" in that the root zone enhances microbial activity, thus increasing the breakdown of organic contaminants (such as petroleum hydrocarbons, PAHs, pesticides, BTEX, chlorinated solvents, PCP, PCBs, and surfactants) in the soil. The rhizosphere extends only about 1 mm from each root. The presence of plant roots moderates soil moisture and increases soil aeration, making conditions more favorable to bioremediation. The production of root exudates, such as sugars, amino acids, and other compounds, stimulates the population growth and activity of native microbes. Root exudates also may serve as food for the microbes, which can result in cometabolism of contaminants as degradation of exudates occurs. Because the microbes consume nutrients, the plants in a rhizodegradation plot often require additional fertilization (USEPA 2006).

Rhizodegradation actually breaks down contaminants; thus, plant harvesting and disposal is not necessary. In some instances, complete mineralization of the contaminant can occur. The success of this technique is site-specific, however, and laboratory microcosms may not reflect the microbial conditions encountered in the field. Petroleum hydrocarbons have been degraded successfully in the rhizosphere, but degradation of aged hydrocarbons has been shown to be more problematic (USEPA 2006).

5.Phytosequestration

Phytosequestration, also referred to as phytostabilization, is a mechanism that immobilizes contaminants, mainly metals, within the root zone, limiting their migration. Immobilization of contaminants can result from adsorption of metals to plant roots, formation of metal complexes, precipitation of metal ions (e.g., due to a change in pH), or a change to a less toxic redox state. Phytosequestration can occur when plants alter the chemical and microbial makeup of the soil (e.g., through the production of exudates or carbon dioxide), which impacts the fate and transport of the soil metals. (USEPA 2006) Although transport proteins within the plant facilitate the transfer of contaminants between cells, plant cells contain a compartment called the vacuole that acts, in part, as a storage and waste receptacle for the plant. The vacuoles of root cells can sequester contaminants, preventing further translocation to the xylem (ITRC 2009).

Because contaminants are retained in the soil, phytosequestration does not require plant harvesting and disposal; however, evaluation of the system is necessary to verify that translocation of contaminants into the plant tissue is not occurring. Due to the continuing presence of contaminants in the root zone, plant health must be monitored and maintained to ensure system integrity and prevent future release of contaminants. Phytosequestration also can be used to prevent migration of soil contaminants with wind and water erosion, soil dispersion, and leaching (USEPA 2006).

6. Phytohydraulics

Phytohydraulics is the ability of vegetation to evapotranspire sources of surface water and groundwater. Water interception capacity by the aboveground canopy and subsequent evapotranspiration through the root system can limit vertical migration of water from the surface downward. The horizontal migration of groundwater can be controlled or contained using deep-rooted species, such as prairie plants and trees, to intercept, take up, and transpire the water. Trees classified as phreatophytes are deep-rooted, high-transpiring, water-loving organisms that send their roots into regions of high moisture and can survive in conditions of temporary saturation. Typical phreatophytes include species such as cottonwoods, poplars, and willows (ITRC 2009).

Source: USEPA. 2006. In Situ Treatment Technologies for Contaminated Soil: Engineering Forum Issue Paper. EPA 542-F-06-013.

ITRC (Interstate Technology & Regulatory Council). 2009. Phytotechnology

Technical and Regulatory Guidance and Decision Trees, Revised. Phyto-3

PIC = Prior Informed Consent
The Rotterdam Convention on Prior Informed Consent (PIC) is a global treaty that came into force in February 2004, with the intention to protect developing countries from the import of dangerous chemicals. The PIC Convention is implemented in the EU by means of regulation concerning the export and import of dangerous chemicals. Under the proposed recast of this PIC Regulation, the companies will continue to notify to their national authorities their intention to export banned or severely restricted chemicals. ECHA will take over the task to communicate with the destination country and to keep a register of the notifications.

Source: News from ECHA, No 5, Oct 2011, http://echa.europa.eu/doc/press/newsletter/echa_newsletter_2011_5.pdf

modern landfills are designed to protect both public health and the environment by providing physical containment of trash, isolation from air and water, and control of landfill gas, leachate, odors, disease vectors, and other nuisances. Modern landfill technology provides hydrologic isolation with various systems of liners and surface capping using compacted clay, plastic membranes, or both; as well as an overlay of about 18 inches of earthen material and at least six inches of soil to support native plant growth and control erosion. Final cover systems are also expected to meet aesthetic and other post-closure site end use criteria for waste management sites. These systems are intended to achieve their functional requirements for time periods of many decades to hundreds of years.

Questions about the long-term performance of the low-permeable layers in conventional cover designs have prompted significant interest and research into alternative designs. Alternative landfill cover systems emerged in the late 1990s as a possible cost-effective option to conventional covers and have been applied at some landfills and other types of waste management units (e.g., waste piles and surface impoundments). The implementation of an alternative cover system is dependent on specific site characteristics. The site characteristics that have a dominant influence on the choice of an appropriate final cover include climate, soils, landfill waste characteristics, hydrogeology, gas production, seismic environment, and reuse of landfill areas.

There are various alternatives to conventional covers. This site focuses on covers that utilize natural processes to manage water precipitating on waste containment sites, commonly known as evapotranspiration (ET) covers. These covers have proven an effective means of containing waste at municipal landfills, hazardous, and industrial waste landfills. There are other types of alternatives to conventional cover systems, such as asphalt barriers. However, these are not addressed on this site because they are not evapotranspiration covers.

ET covers are also known as store and release covers, vegetative covers, sponge and pump covers, alternative final covers (AFC), alternative final earthen covers (AFEC), and other names. They include various combinations of earthen materials and plants, and generally can be categorized into the following cover types:

Monolithic: Any precipitation water is stored in a layer of soil and later removed through evapotranspiration.

Capillary break: This cover uses a two layer system to increase the water storage capacity of the cover. A capillary break is formed by two layers – a layer of fine soil over a layer of coarser material (e.g. sand or gravel). Capillary force causes the layer of fine soil overlying the coarser material to hold more water than if there were no change in particle size between the layers.

Dry barrier: The dry barrier cover uses wind-driven airflow through the layer of coarse material to remove water from a storage layer.

Source: US-EPA, Clu-In: http://www.clu-in.org/products/evap/

EU legislation regulates the marketing and use of plant protection products and their residues in food.

Council Directive 91/414/EEC concerning the placing of plant protection products on the market lays down rules and procedures for approval of the active substances at EU-level and for the authorisation at Member State level of plant protection products (PPPs) containing these substances. This Directive states that substances cannot be used in plant protection products unless they are included in a positive EU list. Once a substance is included in the positive list Member States may authorise the use of products containing them.

Pesticides residues in food are regulated by Regulation (EC) No 396/2005 . The legislation covers the setting, monitoring and control of pesticides residues in products of plant and animal origin that may arise from their use in plant protection. The maximum levels set are those consistent with good agricultural practice in Member States and third countries. The levels are set after an evaluation of any risks to consumers of different age groups and they are only set if they are considered safe. Nonetheless, MRLs (Minimal Risk Level) exceedences are closely monitored, evaluated and communicated to the authorities in the Member States through the Rapid Alert System for Food and Feed whenever there is a potential risk to consumers.

Both Directive 91/414 on the placing on the market of plant protection products and Regulation 396/2005 on pesticide residues in food and feed aim at a high level of protection of human health and the environment.

The European Parliament approved new EU pesticides legislation in January 2009, which will increase the number of pesticides available in Member States, while in due course banning the use of certain dangerous chemicals in these products. Measures to ensure the safer use of pesticides in daily life will also be introduced.

The key points of the new regulation, which deals with the production and licensing of pesticides, are as follows:

• A positive list of approved "active substances" (the chemical ingredients of pesticides) is to be drawn up at EU level. Pesticides will then be licensed at national level on the basis of this list.

• Certain highly toxic chemicals will be banned unless exposure to them would in practice be negligible, namely those which are carcinogenic, mutagenic or toxic to reproduction, those which are endocrine-disrupting, and those which are persistent, bioaccumulative and toxic (PBT) or very persistent and very bioaccumulative (vPvB).

• For developmental neurotoxic and immunotoxic substances, higher safety standards may be imposed.

• If a substance is needed to combat a serious danger to plant health, it may be approved for up to five years even if it does not meet the above safety criteria.

• Products containing certain hazardous substances are to be replaced if safer alternatives are shown to exist. MEPs successfully demanded a shorter deadline for their replacement, of three years rather than five.

• Substances likely to be harmful to honeybees will be outlawed.

see plant protection products directive, 91/414/EEC

plutonic rocks (also called intrusive igneous rocks) resulted from magmas solidified below ground. When magmas crystallize deep underground they look different from volcanic rocks because they cool more slowly and, therefore, have larger crystals. Igneous rocks cooled beneath the Earth's surface are called intrusive rocks. The intrusive equivalents of basalt, andesite, and rhyolite are gabbro, diorite, and granite, respectively. In Hungary the Velencei mountain is composed of intrusive igneous rocks such as, granodiorite and diorite and the granite block in Mórágy was formed in similar conditions.

The underground crystallization stages of the magma are the following:
A. Preliminary crystallization stage (approx. 1100–1000 °C)
During the preliminary crsystallization stage ultrabasic and basic rocks are formed. The temperature decrease results separation of the silicate and sulphide melts. The preliminary crystallization gives economically important ore deposits: chromite, magnetite, ilmenite, platina, diamond and apatite.
B. Main crystallization stage (approx. 1000–700 °C)
In the main crystallization stage the magma solidification occurs. The olivine, pyroxene, amphiboles and the feldspars crystallize in parallel and finally the quartz.
C. Post magmatic stage (from approx. 700 °C)
The volatile containing residual magma is crystallised in this phase. The post magmatic stage includes three phases:

Pegmatite phase (approx. 700–550 °C): The mineral composition of the pegmatites crystallized in this phase is identical with that of the main crystallization phase however the pegmatites contain much larger crystals. The pegmatites in general occur in veins and are rich in rare elements such as stanium, uranium, thorium, boron, lithium, berillium, zirconium, titanium, tanthal.

Pneumatolitic phases (approx. 550–375 °C): The halogene rich solutions are chemically very active and thus are able to considerably modify the solidified rocks. This phase results various minerals such as quartz, fluorite, wolframite, turmaline.

Hydrothermal phase (from approx. 375 °C): The water diluted, solutions of the residual magma penetrated the cracks, voids of the rocks forming hydrothermal veins. During the hydrothermal phase mainly the following metals are concentrated: gold, silver, copper, lead, zinc, mercury and the iron, cobalt and nickel remained still in the residual solution.

the illegal killing of animals or fish, a great concern with respect to endangered or threatened species.

point and non-point sources of water pollution means the sources of pollutants and nutrients the input of which to waters is caused either by locally determined discharges (point source) or by diffuse effects being widespread over the catchment areas (non-point or diffuse sources).

polychlorinated dibenzofurans (PCDFs) are a group of halogenated organic componunds with a furane skeleton and chlor substituents different in numer. PCDFs occur as by-products in the manufacture of chlorinated organic substances, in the incineration of chlorine-containing substances such as PVC, in the bleaching of paper, and also from natural sources such as volcanoes and forest fires. Somilar to polychlorinated dibenzodioxins (PCDDs), they have been shown to bioaccumulate in humans and and animals, are known toxic, mutagenic, carcinogenic and reprotoxic.

the place where a hazardous substance comes from, such as a landfill, waste pond, incinerator, storage tank, or drum. A source of contamination is the first part of an exposure pathway. The source may ba a point or a diffuse source.

the direct or indirect introduction, as a result of human activity, of substances or heat into the air, water or land which may be harmful to human health or the quality of aquatic ecosystems or terrestrial ecosystems directly depending on aquatic ecosystems, which result in damage to material property, or which impair or interfere with amenities and other legitimate uses of the environment.

polychlorinated biphenyls (PCBs) are a class of chlorinated organic compounds, with 1-10 chlorine atoms bound to the biphenyl skeleton, which is the condensate of two benzene rings. The general chemical formula of PCBs is: C₁₂H_10-xCl_x. 

PCBs were used as dielectric fluids in transformers and capacitors, coolants, lubricants, stabilizing additives in flexible PVC coatings of electrical wiring and electronic components, they were used as pesticide extenders, flame retardants, hydraulic fluids, adhesives, anti-dust agents, coating of copy papers, etc.

PCB production was banned in the 1970s due to the high toxicity, mutagenicity and reprotoxicity. They are able to accumulate in the food chain. They are classified as POPs, Persistent organic pollutants.

polychlorinated dibenzodioxins (PCDDs), or simply dioxins, are a group of halogenated organic componunds with a dioxin skeleton and chlor substituents different in numer. Members of the PCDD family have been shown to bioaccumulate in humans and and animals, are known toxic, mutagenic, carcinogenic and reprotoxic. Similar group of toxicants are the the polychlorinated dibenzofurans (PCDFs). Dioxins occur as by-products in the manufacture of chlorinated organic substances, in the incineration of chlorine-containing substances such as PVC, in the bleaching of paper, and also from natural sources such as volcanoes and forest fires.

a polychromatic erythrocyte is an immature erythrocyte in an interstitial phase, that still contains ribosomes, so it can be distinguished from mature erythrocytes by applying selective staining.

PCR is a method for amplifying a DNA base sequence using a heat-stable polymerase and two 20-base primers, one complementary to the (+) strand at one end of the sequence to be amplified and one complementary to the (-) strand at the other end. Because the newly synthesized DNA strands can subsequently serve as additional templates for the same primer sequences, successive rounds of primer annealing, strand elongation, and dissociation produce rapid and highly specific amplification of the desired sequence. PCR also can be used to detect the existence of the defined sequence in a DNA sample.

Source: http://www.ornl.gov/sci/techresources/Human_Genome/glossary/glossary.shtml#modelorganisms

a permeable reactive barrier (PRB) is defined as an in situ method for remediating contaminated ground water that combines a passive chemical or biological treatment zone with subsurface fluid flow management. Treatment media may include zero-valent iron, chelators, sorbents, and microbes to address a wide variety of ground-water contaminants, such as chlorinated solvents, other organics, metals, inorganics, and radionuclides. The contaminants are concentrated and either degraded or retained in the barrier material, which may need to be replaced periodically. There are approximately 100 PRBs operating in the United States and at least 25 internationally.

PRBs can be installed as permanent or semi-permanent units. The most commonly used PRB configuration is that of a continuous trench in which the treatment material is backfilled. The trench is perpendicular to and intersects the ground-water plume. Another frequently used configuration is the funnel and gate, in which low-permeability walls (the funnel) direct the ground-water plume toward a permeable treatment zone (the gate). Some gates are in situ reactors that are readily accessible to facilitate the removal and replacement of reactive media. These PRBs use collection trenches, funnels, or complete containment to capture the plume and pass the ground water, by gravity or hydraulic head, through a vessel containing either a single treatment medium or sequential media. In circumstances where in situ treatment is found to be impracticable, reactive vessels have been located above ground.

Zero-valent iron has performed so successfully in PRB technology that it is now being applied directly for source zone treatment. Though this measure is not considered a PRB, examples of the technology will be included in the PRB pages because the reactive media and treatment mechanism are related. Pneumatic fracturing and injection, hydraulic fracturing, and injection via direct push rigs have been used successfully to introduce the reactive media to the ground-water or soil source area.

Source: US-EPA, Clu-In: http://www.clu-in.org/techfocus/default.focus/sec/Permeable_Reactive_Barriers%2C_Permeable_Treatment_Zones%2C_and_Application_of_Zero-Valent_Iron/cat/Overview/

precautionary principle orientate us in the decision wheather and action should be done or should not be done if the information on the risk is not vaialable or not satisfactory. Precautionary principle should be applied when there is no certain information on risk.

The principle implies that there is a social responsibility to protect the public from exposure to harm, when scientific investigation has found a plausible risk.

Precaution may be defined as "caution in advance," "caution practised in the context of uncertainty," or informed prudence. All definitions have two key elements.

1. an expression of a need by decision-makers to anticipate harm before it occurs. Within this element lies an implicit reversal of the onus of proof: under the precautionary principle it is the responsibility of an activity proponent to establish that the proposed activity will not (or is very unlikely to) result in significant harm.
2. the establishment of an obligation, if the level of harm may be high, for action to prevent or minimise such harm even when the absence of scientific certainty makes it difficult to predict the likelihood of harm occurring, or the level of harm should it occur. The need for control measures increases with both the level of possible harm and the degree of uncertainty.

The European Commission issued a Communication on the precautionary principle in 2000, in which it adopted a procedure for the application of this concept,accepting the Lisbon Treaty advise:

"Union policy on the environment shall aim at a high level of protection taking into account the diversity of situations in the various regions of the Union. It shall be based on the precautionary principle and on the principles that preventive action should be taken, that environmental damage should as a priority be rectified at source and that the polluter should pay."

Fields typically concerned by the precautionary principle are the possibility of:

• Global warming or abrupt climate change in general
• Extinction of species
• Introduction of new and potentially harmful products into the environment, threatening biodiversity (e.g., genetically modified organisms)
• Threats to public health, due to new diseases and techniques (e.g., AIDS transmitted through blood transfusion)
• Long term effects of new technologies (e.g. health concerns regarding radiation from cell phones and other electronics communications devices Mobile phone radiation and health)
• Persistent or acute pollution (asbestos, endocrine disruptors...)
• Food safety (e.g., Creutzfeldt-Jakob disease)
• Other new biosafety issues (e.g., artificial life, new molecules)

The precautionary principle is often applied to biological fields because changes cannot be easily contained and have the potential of being global. The principle has less relevance to contained fields such as aeronautics, where the few people undergoing risk have given informed consent (e.g., a test pilot). In the case of technological innovation, containment of impact tends to be more difficult if that technology can self-replicate. Bill Joy emphasized the dangers of replicating genetic technology, nanotechnology, and robotic technology in his article in Wired Magazine, "Why the future doesn't need us", though he does not specifically cite the precautionary principle. The application of the principle can be seen in the public policy of requiring pharmaceutical companies to carry out clinical trials to showhttp://enfo.hu/mokka/secure/.tmp/glossary/glossary_edit.php that new medications are safe.

The costs and social consequences (increased fear in humans) of the application of the precautionary principle are not clearly beneficial.

Sources:

http://en.wikipedia.org/wiki/Precautionary_principle

Communication from the Commission on the precautionary principle, COM(2000) 1

precautionary statements (P) is part of the Globally Harmonized System of Classification and Labelling of Chemicals (GHS). These arestandardized phrases giving advice about the correct handling of chemical substances and mixtures. P-statement replace the S-phrases, used by DSD (Dangerous Substances Directive).

Precautionary statements are one of the key elements for the labelling of chemical substances and products under the GHS, together with the exact identicifation of the product,hazard pictograms, signal word – either DANGER or WARNING, hazard statements, indicating the nature and degree of the risks posed by the product and the identity of the supplier (manufacturer or importer).

Each precautionary statement is designated a code, starting with the letter P and followed by three digits. Some precautionary phrases are combinations, indicated by a plus sign "+".

General precautionary statements

* P101: If medical advice is needed, have product container or label at hand

* P102: Keep out of reach of children

* P103: Read label before use

Prevention precautionary statements

* P201: Obtain special instructions before use

* P202: Do not handle until all safety precautions have been read and understood

* P210: Keep away from heat/sparks/open flames/hot surfaces – No smoking

* P211: Do not spray on an open flame or other igntion source

* P220: Keep/Store away from clothing/…/combustible materials

* P221: Take any precaustion to avoid mixinn with combustibles

* P222: Do not allow contact with air

* P223: Keep away from any possible contact with water, because of violent reaction and possible flash fire

* P230: Keep wetted with …

* P231: Handle under inert gas

* P232: Protect from moisture

* P233: Keep container tightly closed

* P234: Keep only in original container

* P235: Keep cool

* P240: Ground/bond container and receiving equipment

* P241: Use explosion-proof electrical/ventilating/light/…/equipment

* P242: Use only non-sparking tools

* P243: Take precautionary measures against static discharge

* P244: Keep reduction valves free from grease and oil

* P250: Do not subject to grinding/shock/…/friction

* P251: Pressurized container – Do not pierce or burn, even after use

* P260: Do not breathe dust/fume/gas/mist/vapours/spray

* P261: Avoid breathing dust/fume/gas/mist/vapours/spray

* P262: Do not get in eyes, on skin, or on clothing

* P263: Avoid contact during pregnancy/while nursing

* P264: Wash … thoroughly after handling

* P270: Do not eat, drink or smoke when using this product

* P271: Use only outdoors or in a well-ventilated area

* P272: Contaminated work clothing should not be allowed out of the workplace

* P273: Avoid release to the environment

* P280: Wear protective gloves/protective clothing/eye protection/face protection

* P281: Use personal protective equipment as required

* P282: Wear cold insulating gloves/face shield/eye protection

* P283: Wear fire/flame resistant/retardant clothing

* P284: Wear respiratory protection

* P285: In case of inadequate ventilation wear respiratory protection

* P231+232: Handle under inert gas. Protect from moisture

* P235+410: Keep cool. Protect from sunlight

Response precautionary statements

* P301: IF SWALLOWED:

* P302: IF ON SKIN:

* P303: IF ON SKIN (or hair):

* P304: IF INHALED:

* P305: IF IN EYES:

* P306: IF ON CLOTHING:

* P307: IF exposed:

* P308: IF exposed or concerned:

* P309: IF exposed or you feel unwell:

* P310: Immediately call a POISON CENTER or doctor/physician

* P311: Call a POISON CENTER or doctor/physician

* P312: Call a POISON CENTER or doctor/physician if you feel unwell

* P313: Get medical advice/attention

* P314: Get Medical advice/attention if you feel unwell

* P315: Get immediate medical advice/attention

* P320: Specific treatment is urgent (see … on this label)

* P321: Specific treatment (see … on this label)

* P322: Specific measures (see … on this label)

* P330: Rinse mouth

* P331: Do NOT induce vomiting

* P332: If skin irritation occurs:

* P333: If skin irritation or a rash occurs:

* P334: Immerse in cool water/wrap in wet bandages

* P335: Brush off loose particles from skin

* P336: Thaw frosted parts with lukewarm water. Do not rub affected areas

* P337: If eye irritation persists:

* P338: Remove contact lenses if present and easy to do. continue rinsing

* P340: Remove victim to fresh air and keep at rest in a position comfortable for breathing

* P341: If breathing is difficult, remove victim to fresh air and keep at rest in a position comfortable for breathing

* P342: If experiencing respiratory symptoms:

* P350: Gently wash with soap and water

* P351: Rinse continuously with water for several minutes

* P352: Wash with soap and water

* P353: Rinse skin with water/shower

* P360: Rinse immediately contaminated clothing and skin with plenty of water before removing clothes

* P361: Remove/Take off immediately all contaminated clothing

* P362: Take off contaminated clothing and wash before reuse

* P363: Wash contaminated clothing before reuse

* P370: In case of fire:

* P371: In case of major fire and large quantities:

* P372: Explosion risk in case of fire

* P373: DO NOT fight fire when fire reaches explosives

* P374: Fight fire with normal precautions from a reasonable distance

* P375: Fight fire remotely due to the risk of explosion

* P376: Stop leak if safe to do so

* P377: Leaking gas fire – do not extinguish unless leak can be stopped safely

* P378: Use … for extinction

* P380: Evacuate area

* P381: Eliminate all ignition sources if safe to do so

* <span class="abbr" style="color: blue; border-bottom: 1px dotted blue" title="Error in hazard statements">P391: Collect spillage

* P301+310: IF SWALLOWED: Immediately call a POISON CENTER or doctor/physician

* P301+312: IF SWALLOWED: Call a POISON CENTER or doctor/physician if you feel unwell

* P301+330+331: IF SWALLOWED: Rinse mouth. Do NOT induce vomiting

* P302+334: IF ON SKIN: Immerse in cool water/wrap in wet bandages

* P302+350: IF ON SKIN: Gently wash with soap and water

* P302+352: IF ON SKIN: Wash with soap and water

* P303+361+353: IF ON SKIN (or hair): Remove/Take off immediately all contaminated clothing. Rinse skin with water/shower

* P304+312: IF INHALED: Call a POISON CENTER or doctor/physician if you feel unwell

* P304+340: IF INHALED: Remove victim to fresh air and keep at rest in a position comfortable for breathing

* P304+341: IF INHALED: If breathing is difficult, remove victim to fresh air and keep at rest in a position comfortable for breathing

* P305+351+338: IF IN EYES: Rinse continuously with water for several minutes. Remove contact lenses if present and easy to do – continue rinsing

* P306+360: IF ON CLOTHING: Rinse immediately contaminated clothing and skin with plenty of water before removing clothes

* P307+311: IF exposed: Call a POISON CENTER or doctor/physician

* P308+313: IF exposed or concerned: Get medical advice/attention

* P309+311: IF exposed or you feel unwell: Call a POISON CENTER or doctor/physician

* P332+313: If skin irritation occurs: Get medical advice/attention

* P333+313: If skin irritation or a rash occurs: Get medical advice/attention

* P335+334: Brush off loose particles from skin. Immerse in cool water/wrap in wet bandages

* P337+313: Get medical advice/attention

* P342+311: Call a POISON CENTER or doctor/physician

* P370+376: In case of fire: Stop leak if safe to do so

* P370+378: In case of fire: Use … for extinction

* P370+380: In case of fire: Evacuate area

* P370+380+375: In case of fire: Evacuate area. Fight fire remotely due to the risk of explosion

* P371+380+375: In case of major fire and large quantities: Evacuate area. Fight fire remotely due to the risk of explosion

Storage precautionary statements

* P401: Store …

* P402: Store in a dry place

* P403: Store in a well ventilated place

* P404: Store in a closed container

* P405: Store locked up

* P406: Store in a corrosive resistant/… container with a resistant inner liner

* P407: Maintain air gap between stacks/pallets

* P410: Protect from sunlight

* P411: Store at temperatures not exceeding … °C/… °F

* P412: Do not expose to temperatures exceeding 50 °C/122 °F

* P420: Store away from other materials

* P422: Store contents under …

* P402+404: Store in a dry place. Store in a closed container

* P403+233: Store in a well ventilated place. Keep container tightly closed

* P403+235: Store in a well ventilated place. Keep cool

* P410+403: Protect from sunlight. Store in a well ventilated place

* P410+412: Protect from sunlight. Do not expose to temperatures exceeding 50 °C/122 °F

* P411+235: Store at temperatures not exceeding … °C/… °F. Keep cool

Disposal precautionary statements

* P501: Dispose of contents/container to ..

precision of a measurement system, also called reproducibility or repeatability, is the degree to which repeated measurements under unchanged conditions show the same results.

The precision of a measurement system, also called reproducibility or repeatability, is the degree to which repeated measurements under unchanged conditions show the same results.Although the two words reproducibility and repeatability can be synonymous in colloquial use, they are deliberately contrasted in the context of the scientific method.

A measurement system can be accurate but not precise, precise but not accurate, neither, or both. For example, if an experiment contains a systematic error, then increasing the sample size generally increases precision but does not improve accuracy. The result would be a consistent yet inaccurate string of results from the flawed experiment. Eliminating the systematic error improves accuracy but does not change precision.

A measurement system is designated valid if it is both accurate and precise. Related terms include bias (non-random or directed effects caused by a factor or factors unrelated to the independent variable) and error (random variability).

Source: http://en.wikipedia.org/wiki/Accuracy_and_precision

The precision of a measurement system, also called reproducibility or repeatability, is the degree to which repeated measurements under unchanged conditions show the same results.

Precision shoul be distingueshed from accuracy.

A measurement system can be accurate but not precise, precise but not accurate, neither, or both.

For example, if an experiment contains a systematic error, then increasing the sample size generally increases precision but does not improve accuracy. The result would be a consistent yet inaccurate string of results from the flawed experiment. Eliminating the systematic error improves accuracy but does not change precision.

predictable death is a term used in toxicity tests when the presence of clinical signs indicative of death at a known time in the future before the planned end of the experiment, for example: inability to reach water or food.

concentration of the substance below which adverse effects in the environmental sphere of concern are not expected to occur. PNEC is relevant for an ecosystem, e.g. aquatic or terrestrial. PNEC is generally calculated from the ecotoxicity test results of testorganisms of three different trophic levels by factorial extrapolation, using safety factors or by statistical extrapolation.

Applying factorial extrapolation the following assessment factors are applied according to uniform protocols:

f=1000: at least one short-term EC50 from each of three trophic levels,
f = 100: long-term NOEC from one trophic level besides 2 acute,
f = 50: long-term NOEC from species representing two trophic levels besides one acute,
f = 10: long-term NOEC from at least three trophic levels,
f = 1: PNEC can be directly measured in microcosms, mesocosms or ecosystem-field-testing.

Another method to determine a PNEC value is the use of statistical extrapolation methods using the variation in species sensitivity. If a large data set with NOECs from long-term experiments for different taxonomic groups is available, these values can be used to draw a distribution. This distribution that describes the variability of hazard of a substance to organisms is called a Species Sensitivity Distribution (SSD). This distribution can be presented as a frequency distribution (cumulative normal distribution curves or other similar distribution curves) of NOEC values for species. From this curve we can read Xm, the mean toxicity expressed as the mean NOEC value of a substance. The Sm represents the toxicity range or variation in sensitivity of a substance.

The main assumption on the use of SSDs in risk assessment is that the distribution based on a selection of species (tested in laboratory experiments) are representative for all species (in the field).

Statistical extrapolation methods may be used to derive a PNEC from a SSD by taking a prescribed percentile of this distribution. For pragmatic reasons it has been decided that the concentration corresponding with the point in the SSD profile below which 5% of the species occur, should be derived as an intermediate value in the determination of a PNEC. This 5% point in the SSD is also identified as a hazardous concentration (HC) at which a certain percentage (in this case 5%) of all species is assumed to be affected.