Joel R. Coats

Comparative toxicology of the pyrethroid insecticides

The toxic effects elicited by synthetic pyrethroids in animals are varied in degree and nature. Their relative safety to birds and mammals contrasts sharply with their acute effects on fish and arthropods. Explantation of their differences in toxicity depends on examination of all factors of their comparative toxicology. Routes of exposure are important, as are metabolism and elimination rates, especially for mammals and birds with their considerable capabilities for biotransformation. Significant differences in sensitivity at the sites of toxic action may also play a role in differential responses to these insecticides. Finally, physical properties that influence the environmental disposition and subsequently affect bioavailability of the compounds in water, soil, air, produce, and nontarget species are also instrumental in determining the impact of current and future synthetic pyrethroid insecticides.

Chlorpyrifos: Ecological Risk Assessment in North American Aquatic Environments

The objective of this risk assessment was to determine the probability and significance of effects of the organophosphate insecticide, chlorpyrifos, on aquatic ecosystems in North America. The assessment addressed both agricultural and nonagricultural uses. However, the primary focus of the risk assessment was agricultural ecosystems, especially row crops and, in particular, the “corn-belt” agroecosystems. The risk assessment also addressed potential effects from other agricultural uses as well as urban uses such as turf, termiticide, and home use. Exposure and effects in freshwater and saltwater environments were considered. Aquatic invertebrates and fish were included in the assessment, but amphibians, reptiles, birds, and mammals were not. The potential exposure of these organisms is small because of a lack of biomagnification of chlorpyrifos. Thus, if their prey are not affected, it is unlikely that organisms at higher trophic levels would be adversely affected. Measurements of chlorpyrifos residues in fish have shown both low probability and low concentrations of exposure (USEPA 1992b). Insufficient data on amphibians were available for a direct assessment of risks. A risk assessment of chlorpyrifos in terrestrial ecosystems was conducted in parallel with this aquatic risk assessment (Kendall et al., in manuscript). Chlorpyrifos is not used in isolation, and residues of other substances with the same mechanism of action may co-occur with chlorpyrifos and some of these may display additive toxicity (Bailey et al. 1997). Although the presence of these compounds could influence the overall conclusions of a risk assessment for the class of anticholinesterase insecticides, the extensive resources necessary to conduct a classwide review were not available and they were excluded from this evaluation.

Phytoremediation—An Overview

The use of plants (directly or indirectly) to remediate contaminated soil or water is known as phytoremediation. This technology has emerged as a more cost effective, noninvasive, and publicly acceptable way to address the removal of environmental contaminants. Plants can be used to accumulate inorganic and organic contaminants, metabolize organic contaminants, and encourage microbial degradation of organic contaminants in the root zone. Widespread utilization of phytoremediation can be limited by the small habitat range or size of plants expressing remediation potential, and insufficient abilities of native plants to tolerate, detoxify, and accumulate contaminants. A better understanding and appreciation of the potential mechanisms for removing contaminants from the root zone and the interaction between plants, microorganisms, and contaminants will be useful in extending the application of phytoremediation to additional contaminated sites.

Enhanced degradation of a mixture of three herbicides in the rhizosphere of a herbicide-tolerant plant

Abstract The rhizosphere of herbicide-tolerant plants may be an important component in biologically remediating pesticide-contaminated soils. A pesticide-contaminated site at an agrochemical dealership in Iowa was characterized, and soil from the site was brought to the laboratory for degradation experiments. Three major herbicides were identified in the soils by gas chromatography-atrazine, metolachlor, and trifluralin. Although concentrations of these chemicals were as high as 2 to 3 times field application rates, herbicide-tolerant plants were found growing in the contaminated soil. Initial numbers of microorganisms were determined in rhizosphere soil from Kochia sp. and in edaphosphere (nonvegetated) soil. The rhizosphere soil had an order of magnitude higher microbial numbers (4.2 × 10 5 ) compared with the edaphosphere soil (3.5 × 10 4 .) A degradation experiment that did not incorporate vegetation was carried out by using sterile control soil, Kochia sp. rhizosphere soil, and edaphosphere soil spiked with a mixture of atrazine, metolachlor, and trifluralin at levels typical of point-source spills. Significantly (p ≤ 0.10) enchanced degradation was observed in the rhizosphere soil after 14-d incubations. Microorganisms in nonvegetated soil also showed the ability to degrade the three compounds, but not to the extent of the rhizosphere soil. Some abiotic degradation occurred for all three herbicides. The results of these preliminary experiments suggest that the rhizosphere of certain plant species may be important for facilitating microbial degradation of pesticide wastes in soils and beneficial for remediating pesticide-contaminated sites.

Insect repellents - past, present and future

Chris Peterson and Joel Coats from the Department of Entomology at Iowa State University, USA, review the history of insect repellents from the 1920s down to recent work on plant-derived repellents.

Application of the Microtox System to Assess the Toxicity of Pesticides and Their Hydrolysis Metabolites

In this study, we used the Microtox analyzer to determine the relative microbial toxicities of some pesticides and their metabolites. Because hydrolysis is a significant step in the chemical and microbial degradation of pesticides in soil, the principal focus of this investigation was on hydrolytic metabolites

Adult Repellency and Larvicidal Activity of Five Plant Essential Oils Against Mosquitoes

ABSTRACT The larvicidal activity and repellency of 5 plant essential oils—thyme oil, catnip oil, amyris oil, eucalyptus oil, and cinnamon oil—were tested against 3 mosquito species: Aedes albopictus, Ae. aegypti, and Culex pipiens pallens. Larvicidal activity of these essentials oils was evaluated in the laboratory against 4th instars of each of the 3 mosquito species, and amyris oil demonstrated the greatest inhibitory effect with LC50 values in 24 h of 58 µg/ml (LC90  =  72 µg/ml) for Ae. aegypti, 78 µg/ml (LC90  =  130 µg/ml) for Ae. albopictus, and 77 µg/ml (LC90  =  123 µg/ml) for Cx. p. pallens. The topical repellency of these selected essential oils and deet against laboratory-reared female blood-starved Ae. albopictus was examined. Catnip oil seemed to be the most effective and provided 6-h protection at both concentrations tested (23 and 468 µg/cm2). Thyme oil had the highest effectiveness in repelling this species, but the repellency duration was only 2 h. The applications using these natural product essential oils in mosquito control are discussed.

Plant growth regulatory effect and insecticidal activity of the extracts of the Tree of Heaven ( Ailanthus altissima L.)

BackgroundThere is an urgent need to explore and utilize naturally occurring products for combating harmful agricultural and public health pests. Secondary metabolites in the leaves of the Tree of Heaven, Ailanthus altissima L. have been reported to be herbicidal and insecticidal. The mode of action, however, of the active compounds in A. altissima are not understood. In this paper, we report the chemical characteristics of the herbicidal and insecticidal components in this tree, and will discuss the effect of light on the bioactivity of the active components.ResultsExtracts from the fresh leaves of A. altissima showed a strong plant germination/growth inhibitory effect in laboratory bioassays against alfalfa (Medicago sativa). The effect was dose-dependent. The growth inhibitory components were in the methylene chloride soluble fraction of the extract. The effect was greater in the light than in the dark. Other fractions had plant growth enhancing effect at lower concentrations. The extract was slightly insecticidal against yellow fever mosquito larvae (Aedes aegypti).ConclusionsThe extract or its semi-purified fractions of A. altissima were strong plant growth inhibitors, therefore good candidates as potential environmentally safe and effective agricultural pest management agents. The finding that light affects the activity will be useful in the application of such natural products.

Degradation of chlorpyrifos and its hydrolysis product, 3,5,6‐trichloro‐2‐pyridinol, in soil

The degradation of 14C‐chlorpyrifos and its hydrolysis product, 3,5,6‐trichloro‐2‐pyridinol (TCP), was investigated in soil in laboratory experiments. Between 12 and 57% of the applied chlorpyrifos...

Physiological response of rainbow trout (Salmo gairdneri) to acute fenvalerate intoxication

Abstract The physiological responses of rainbow trout ( Salmo gairdneri ) to fenvalerate intoxication during aqueous exposure were examined to provide information about the pyrethroid mode of action in fish. Trout ( n = 4) were exposed to 412 ± 50 μg/liter fenvalerate and died in 10.9 ± 1.5 hr. Brain, liver, and carcass fenvalerate concentrations associated with mortality were 0.16 ± 0.05, 3.62 ± 0.57, and 0.25 ± 0.05 mg/kg, respectively. Visible signs of intoxication included elevated cough rate, tremors, and seizures. Histopathological examination of gill tissue showed damage consistent with irritation. An evaluation of respiratory-cardiovascular and blood chemistry responses indicated an elevated rate of metabolism associated with increasingly severe seizures. A cessation of ventilatory and cardiac activity, occurring with the seizures, was also observed. Finally, urine osmolality, Na + and K + concentrations, and Na + and K + excretion rates were elevated with intoxicated trout. The physiological responses of rainbow trout to fenvalerate intoxication suggest that besides effects on the nervous system, effects on respiratory surfaces and renal ion regulation may be associated with the mechanism of pyrethroid action in fish.