Population level effects herbicides

Significant levels of herbicides have also been detected in rivers, although these are usually transitory. Heavy rainfall can move herbicides from agricultural land to nearby ditches and streams due to runoff, and in soils that are high in clay, percolation of water occurs through deep fissures with consequent movement into neighboring water courses. Such events under extreme weather conditions are likely to have contributed to the pulses of herbicide contamination observed in some rivers. Questions have been asked about possible effects of such episodic pollution on populations of aquatic plants. 

FIFRA microcosm experimental unit. An example of a microcosm experimental unit designed to test the effects of a herbicide on an aquatic environment. This particular setup does not include fish since the predatory effects would tend to hide lower trophic level effects upon the invertebrate populations. Typically, a FIFRA microcosm experiment includes fish species, especially when acetylcholinesterase inhibitors or other toxicants particularly effective against animal species are tested. 

These high levels were sporadic and transitory. However, some of them were high enough to have caused phytotoxicity, and more work needs to be done to establish whether herbicides are having adverse effects upon populations of aquatic plants in areas highlighted in this study. It should also be borne in mind that there may have been additive or synergistic effects caused by the combinations of herbicides found in these samples. For example, urea herbicides such as diuron and chlortoluron act upon photosynthesis by a common mechanism, so it seems likely that any effects upon aquatic plants will be additive. Similarly, simazine and atrazine share a common mechanism of action. 

Interaction effects of mercury with other contaminants, such as herbicides and pesticides, could intensify hazards to avian populations (Mullins et al. 1977). For example, a striking parallel exists between levels of Hg and of DDT and its metabolites in birds of prey, suggesting the existence of common ecotoxicological mechanisms (Delbeke et al. 1984 Wiemeyer et al. 1984) additional research is clearly needed. 

Intermediate-Duration Exposure. Intermediate-duration exposure of humans to CDDs has occurred after industrial accidents or in population groups (e g., Vietnam veterans, Vietnamese, and pesticide production workers and applicators) exposed to CDD-contaminated herbicides. As stated above, the route of exposure and exposure levels cannot be exactly determined. Hepatic and dermal changes were the main effects noted, and an association between incidence of diabetes and exposure to... 

Many industrial accidents involving malfunctioning reaction vessels used to manufacture chlorinated phenols or phenoxy herbicides have exposed more than 1300 workers to shortterm, high-level doses of the dioxins that occur as contaminants of these substances. Exposures have frequently been associated with acne-like skin lesions, dermatitis, altered liver enzyme concentrations, pulmonary deficiency, numbness, nausea, headache, hearing loss, sleep disturbance, tiredness, sexual dysfunction, depression, and appetite loss. Populations exposed to dioxin-contaminated materials through non-occupational sources - including (hoxin-contaminated soils in Missouri, a trichlorophenol reactor explosion in Italy, dioxin-containing herbicide in Viemam, and assorted laboratory accidents - have all experienced similar effects. 

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