Toxic Effects in the Field

Inevitably, terrestrial invertebrates are susceptible to the toxicity of OPs used in the field. The honeybee is one species of particular importance, and the use of OPs and other insecticides on agricultural land has been restricted to minimize toxicity to this species. One practice has been to avoid application of hazardous chemicals to crops when there are foraging bees. The use of some compounds, for example, triazophos, has been restricted because of very high toxicity to honeybees. 

As noted earlier, OPs are known to be highly toxic to aquatic invertebrates and to fish. This has been demonstrated in field studies. For example, malathion applied to watercress beds caused lethal intoxication of the freshwater shrimp Gammarus pulex located downstream (Crane et al. 1995). Kills of marine invertebrates have been reported following the application of OPs. Accidental release of OPs into rivers, lakes, and bays has sometimes caused large-scale fish kills (see Environmental Health Criteria 63). 

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The cyclodiene insecticides aldrin, dieldrin, endrin, heptachlor, endosulfan, and others were introduced in the early 1950s. They were used to control a variety of pests, parasites, and, in developing countries, certain vectors of disease such as the tsetse fly. However, some of them (e.g., dieldrin) combined high toxicity to vertebrates with marked persistence and were soon found to have serious side effects in the field, notably in Western European countries where they were extensively used. During the 1960s, severe restrictions were placed on cyclodienes so that few uses remained by the 1980s. 

Bioindicators of effect in the field such as intersex index (ISI) and population decline in gastropods are useful to reveal causal relationships between the exposure to toxic compounds and population effects on local marine organisms. When these effects correspond to the effects predicted based on bioassays in the laboratory, for example expressed as PAF of species, these field effects in gastropods, can be used as a bioindicator for the local ecotoxicological health status. 

Subsequent experiments by the Allies provi tl that diphcnylchlor-arsine was extremely effective in the field when dispersed (by heat distillation) as a true toxic smoke, and they were preparing toxic smoke candles, embodying this principle of dispersion, wlien the Armistiw intervened and prevented their use at the front. The failure to adopt a proper means of dispersing diphenylchlorarsine stands out as one of the few technical mistakes in chemical warfare that the Germans made dur-... 

The outcome of the risk assessment is expressed in real-world effects instead of a toxicity exposure ratio (TER) number, for which it is unclear how protective it is in terms of effects in the field. 

The STAGS is a customer funded development that was designed to support the US Army Alternative Technologies to Incineration s Ton Container Survey. To date, only a part of this mission has been accomplished. As successful as the NAAP analysis of VX has been, it is obvious that we face new challenges as we move ahead to Tooele Army Depot, other storage facilities and toxic waste sites. It is the opion of this author that the STAGS has proven itself safe and effective for characterizing super toxic materials in the field and that it will serve a useful purpose and suceed in all of it s future missions. 

The scientific and technical corrosion literature has descriptions and lists of numerous chemical compounds that exhibit inhibiting properties. Of these only a very few are ever actually used in practical systems. This is partly due to the fact that in practice the desirable properties of an inhibitor usually extend beyond those simply relating to metal protection. Thus cost, toxicity, availability, etc. are of considerable importance as well as other more technical aspects (see Principles). Also, as in many other fields of scientific development, there is often a considerable time lag between laboratory development and practical application. In the field of inhibition the most notable example of this gap between discovery and application is the case of sodium nitrite. Originally reported in 1899 to have inhibitive properties, it remained effectively unnoticed until the 1940s it is now one of the most widely employed inhibitors. 

Essential oils are known to have detrimental effects on plants. The inhibitory components have not been identified, but both alde-hydic (benzol-, citrol-, cinnamal-aldehyde) and phenolic (thymol, carvacol, apiol, safrol) constituents are suspected. Muller et al. (104) demonstrated that volatile toxic materials localized in the leaves of Salvia leucophylla, Salvia apiana, and Arthemisia californica inhibited the root growth of cucumber and oat seedlings. They speculated that in the field, toxic substances from the leaves of these plants might be deposited in dew droplets on adjacent annual plants. In a subsequent paper, Muller and Muller (105) reported that the leaves of S. leucophylla contained several volatile terpenes, and growth inhibition was attributed to camphor and cineole. 

Most of the toxic effects caused by methyl parathion resulted from exposure by multiple routes, especially for workers in sprayed fields or formulating facilities, or people in homes. Dean et al. (1984) reported deaths and toxic effects in several children as well as lowered blood cholinesterase levels and excretion of urinary 4-nitrophenol (adults showing no adverse effects also excreted 4-nitrophenol). 

In environmental risk assessment, the objective is to establish the likelihood of a chemical (or chemicals) expressing toxicity in the natural environment. Assessment is based on a comparison of ecotoxicity data from laboratory tests with estimated or measured exposure in the field. The question of effects at the level of population that may be the consequence of such toxicity is not addressed. This issue will now be discussed. 

Another issue is the development and refinement of the testing protocols used in mesocosms. Mesocosms could have a more important role in environmental risk assessment if the data coming from them could be better interpreted. The use of biomarker assays to establish toxic effects and, where necessary, relate them to effects produced by chemicals in the field, might be a way forward. The issues raised in this section will be returned to in Chapter 17, after consideration of the individual examples given in Part 2. 

A central theme of this text is the development of biomarker assays to measure the extent of toxic effects caused by chemicals both in the field studies and for the purposes of environmental risk assessment. 

In 1868 two Scottish scientists, Crum Brown and Fraser [4] recognized that a relation exists between the physiological action of a substance and its chemical composition and constitution. That recognition was in effect the birth of the science that has come to be known as quantitative structure-activity relationship (QSAR) studies a QSAR is a mathematical equation that relates a biological or other property to structural and/or physicochemical properties of a series of (usually) related compounds. Shortly afterwards, Richardson [5] showed that the narcotic effect of primary aliphatic alcohols varied with their molecular weight, and in 1893 Richet [6] observed that the toxicities of a variety of simple polar chemicals such as alcohols, ethers, and ketones were inversely correlated with their aqueous solubilities. Probably the best known of the very early work in the field was that of Overton [7] and Meyer [8], who found that the narcotic effect of simple chemicals increased with their oil-water partition coefficient and postulated that this reflected the partitioning of a chemical between the aqueous exobiophase and a lipophilic receptor. This, as it turned out, was most prescient, for about 70% of published QSARs contain a term relating to partition coefficient [9]. 

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