Chemicals persistent

Exposure of wildlife to EDs also occurs via their food and in most ecosystems there is a tendency for persistent chemicals to bioaccumulate and biomagnify organisms higher up the food chain accumulate more of the chemical than those... 

The other global environmental problem, stratospheric ozone depletion, was less controversial and more imminent. The U.S. Senate Committee Report supporting the Clean Air Act Amendments of 1990 states, Destruction of the ozone layer is caused primarily by the release into the atmosphere of chlorofluorocarbons (CFCs) and similar manufactured substances—persistent chemicals that rise into the stratosphere where they catalyze the destruction of stratospheric ozone. A decrease in stratospheric ozone will allow more ultraviolet (UV) radiation to reach Earth, resulting in increased rates of disease in humans, including increased incidence of skin cancer, cataracts, and, potentially, suppression of the immune system. Increased UV radiation has also been shown to damage crops and marine resources."... 

Any hazard which land deposition may create requires assessment with regard to the risk of injury or impairment of health to persons or animals, damage to vegetation, pollution of controlled waters including aquifers - eitlier duectly or because of water run-off, and of long-tenu accumulation, e.g. of heavy metals or persistent chemicals. 

Schwebstoff, m, = Schwebestoff (Mil.) non-persistent chemical agent, -filter, n. filter for suspended material. 

Neurotoxic compounds can have behavioral effects in the field (see Chapters 5, 9, and 15), and these may reduce the breeding or feeding snccess of animals and their ability to avoid predation. A number of the examples that follow are of sub-lethal effects of pollutants. The occurrence of sublethal effects in natural populations is intimately connected with the question of persistence. Chemicals with long biological half-lives present a particular risk. The maintenance of substantial levels in individuals, and along food chains, over long periods of time maximizes the risk of sublethal effects. Risks are less with less persistent compounds, which are rapidly... 

Jobling, S., Reynolds, T., and White, R. et al. (1995). A variety of environmentally persistent chemicals, including some phthalate plasticizers, are weakly estrogenic. Environmental Health Perspectives 103, 582-587. 

Huey C, Brinckman FE, Grim S, Iveson WP (1974) In Freitas ASW, Kushner DJ, Quadri DSU (eds) Proceedings of the international conference on the transport of persistent chemicals in aquatic ecosystems. National Research Council of Canada, Ottawa, pp 11-73—11-78... 

C. Huey, F. E. Brinckman, S. Grim and W. P. Iverson, Proc. Int. Conf. Transport Persist Chemicals Aquat. Ecosystems, Ottawa, 1974, N.R.C. Canada, p. 11-73. 

Because PCDD/Fs became to be recognized as the most hazardous for the environment and human beings, very restricted emission limits were introduced in the most countries. But only a few countries limits are also pursuit for PCDD/F levels in sewage sludge, however sludge is one of the ultimate sinks for persistent chemicals. 

The new Polish Waste Act (issued May 2001) strictly regulates sludge application. The disposal of sludge to the land used for vegetable cultivation as well as to pastures and meadows is prohibited, what minimizes the possibility for persistent chemicals to enter the food chain. 

It is briefly reported that flame retardants were among the chemicals discovered in the blood of Margot Wallstrom, European Commissioner for the Environment. Wallstrom submitted a sample for testing to illustrate the presence of persistent chemicals in the human body. The Department of Environmental Sciences at Lancaster University tested for the presence of 77 man-made chemicals. The laboratory discovered 28 chemicals in Wallstrom s blood, including polybrominated diphenyl ethers, commonly used as flame retardants. 

The chlorinated chemicals assessed do not have the same risk profile. For the more volatile chemicals the safety margins between the actual exposure and the level at which no effect on the environment would be expected is quite high. For more persistent chemicals there is a need to look to the environmental compartment where they can be accumulated (mainly in sediments and biota). For some of these chemicals the safety margin is quite low and in worst-case situations serious effects may occur. For the very persistent, bioaccumulative and toxic chemicals (like dioxins, PCBs and DDT), acceptable environmental concentrations are so low and difficult to control that the industry is committed to reducing as far as possible releases to the environment through application of Best Available Techniques (BAT), mainly with respect to dioxins. For other chemicals (PCBs, DDT), production has already been halted for some years. 

Cote MG, Plaa GL, Valli VE, et al. 1985. Subchronic effects of a mixture of persistent chemicals found in the Great Lakes. Bull Environ Contam Toxicol 34(2) 285-290. 

This does not necessarily mean, however, that the risks of lawn care are necessary or inherent to the larger lawn economy. The continued innovation of treatments, after all, is generally hailed by industry as a victory for chemistry that has led to decreased risk. DDT is arguably less hazardous than lead arsenate, or at least more efficient. Discovery of the hazards of DDT led to less persistent chemicals. Glyphosate is likely more benign than 2,4-D, and so on. 

Elimination rates are commonly expressed as half-lives, the time required for half the amount of a chemical to leave the body. Half-lives for rapidly eliminated chemicals are typically in the range of a few hours. Highly persistent chemicals (see below) have half-lives of years. 

The so-called persistent organic pollutants (POPs) are the subject of the Rio Declaration (1994) and the Stockholm Convention (2001) these international agreements (yet to be ratified in all signatory countries, including the United States) call for the elimination from production of 12 persistent chemicals, including the chlorinated pesticides and PCBs mentioned above (all of which have already been eliminated from production in the United States). Current regulatory efforts in the European Union and the United States place emphasis on elimination or restriction of all PBTs (persistent, bioaccumulative, and toxic chemicals). 

It is not possible to achieve "adequate control" of the risks of persistent, bioaccumulative chemicals. The fact that traditional risk assessment cannot reasonably be applied to such chemicals, and that a revised PBT (persistent, bioaccumulative, toxic) assessment is necessary, is explicitly recognised in the EU s Technical Guidance Document for risk assessment. Their intrinsic properties mean that there is a high risk of exposure at sometime during the lifecycle of the chemical or the article that contains it. Even small releases, if they are continuous, can result in significant exposures. This is why we see significant and, in some cases, escalating levels of brominated flame retardants, nonylphenols and other persistent chemicals in breast milk, umbilical cord blood and human tissue. 

Leuenberger, C., Giger, W., Coney, R., Graydon, J.W., and Molnar-Kubica, E. Persistent chemicals in pulp mill effluents. Occurrence and behaviour in an activated sludge treatment plant. Water Res., 19(7) 885-894, 1985. 

But even a small-scale trial-and-error strategy has to be organised within society. As discussed in the previous section, iimovations are rather improbable and disadvantaged by stractural frameworks. Iimovations depend upon freedom for them to be developed. At the same time safety barriers have to be formulated within which the search process can move freely. For example, possible environmental effects must be anticipated, necessitating controlled release in small increments and retrievability must be ensured. (Quantitative and qualitative restrictions must be imposed so that retrieval and repair options can still be effective if a trial is aborted. This approach is more successful if the persistence and spatial range of a chemical is low than for persistent chemicals like CFCs and PCBs. This requires that limited Teaming spaces or experimentation spaces have to be created intentionally under technical and economic risk considerations. Small increments and a steady increase are to be preferred, accompanied by intensive monitoring of detectable consequences. 

The effect of any chemical at a biological target depends on its ability to attain a target site concentration that exceeds the threshold required to ehcit the response. The intensity and duration of the response depends on the toxicokinetic properties of the compound (absorption, distribution, metabolism, and excretion) and the nature of the target site interaction (reversible, irreversible). If recovery is complete between successive exposures, no cumulative toxicity is to be expected. However, a short-term acute exposure could potentially add to the long-term burden of a persistent chemical and be relevant for the magnitude of the chronic effect. 

A relative term referring to an intermediate in a reaction or series of reactions which is short-lived under the given experimental conditions and assay procedures. Such species have a shorter half-life than persistent chemical species. 

It turns out that most of these compounds have similar characteristics that contribute to their toxicity to both humans and other species of plants and animals. First, the compounds are environmentally persistent. Many of the early pesticides, and certainly the metals, do not break down in the environment or do so only very slowly. If persistent chemicals are released continually to the environment, the levels tend to rise ever higher. This means they are available to cause harm to other organisms, often not even the target of the pesticide. Second, the early pesticides were broad acting and toxic to many species, not just the target species. These poisons often killed beneficial insects or plants. Third, many of these compounds would bioaccumulate or concentrate in species as they moved up the food chain. The chlorinated pesticides accumulate in the fat of animals. Animals that consumed other animals accumulated more and more of these pesticides. Most species could not metabolize or break down the compounds. Lead accumulates in bone and methyl mercury in muscle. And finally, because of their persistence in the environment and accumulation in various species, the persistent toxicants spread around the world even to places that never used them. Animals at the top of the food chain, such as polar bears and beluga whales, routinely have fat PCB levels greater that 6 ppm. 

WTC provides information on model pesticide-policies, alternatives to home pesticides, information on persistent chemical pollutants, and much more. 

Probably the greatest concern in the workplaces is solvent exposure from cleaning agents or chemical processes. Farmers and pesticide workers can also be exposed to compounds clearly designed to affect the nervous system. The outdoor environment can contain elevated levels of a number of persistent chemicals that can adversely affect the nervous system, such as lead, mercury, and chlorinated pesticides. 

Toxaphene, or polychlorocamphene (CioHioCls), is a pesticide for cotton. It has no significant biodegradation or photolysis reactions in the environment, so it is a persistent chemical. Henry s law constant for toxaphene is Ht = 6.0 x 10 atm m /mole. The initial conditions are given in Figure E8.5.1. 

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