Temperature as a toxicity identification evaluation tool for pyrethroid insecticides: Toxicokinetic confirmation

Abstract

Toxicity identification evaluation (TIE) methods can be used to identify toxic compounds in environmental samples using a variety of laboratory techniques. Whereas TIEs exist for nonpolar organics, relatively few methods are established for individual contaminant classes. Toxicity identification evaluations have shown pesticides to be the cause of toxicity in agricultural waters and effluents, and more recent studies have shown that the insecticide class of concern is pyrethroids. The primary objectives of the present study were to confirm a temperature TIE model and mechanistically explain these trends. This was achieved by comparing the relative toxicity and influence of temperature (13 vs. 23 degrees C) on Chironomus dilutus exposed to four insecticides, including two pyrethroids, an organophosphate, and an organochlorine, and then explaining these changes using toxicokinetics. A 10 degrees C temperature decrease increased the toxicity of pyrethroids and DDT but decreased the toxicity of chlorpyrifos. The decrease in chlorpyrifos toxicity was driven primarily by the reduction of the formation of more toxic products via decreased biotransformation. The increase in DDT toxicity, in contrast, can be attributed to increased nerve sensitivity at 13 versus 23 degrees C. The pyrethroid toxicity change, however, resulted from a combination of increased accumulation of parent compound and increased nerve sensitivity, exacerbating the toxicity of pyrethroids at 13 degrees C. These trends also held true in sediment exposures with chlorpyrifos and permethrin, indicating that water-only exposures were adequate substitutes for examining this mechanism.

Life Histories, Salinity Zones, and Sublethal Contributions of Contaminants to Pelagic Fish Declines Illustrated with a Case Study of San Francisco Estuary, California, USA

“…Physical effects of DDT, also a neurotoxin, increase at lower temperatures because nerve sensitivity increases ). Conversely, raising water temperature by 1°C to 2°C caused 1.5-to 100-fold increases in the toxicity of metals, carbamates, organophosphates (including chlorpyrifos), and some organochlorines other than DDT (Lydy et al 1990;Boening 2000;Heugens et al 2001;Harwood et al 2009). Large increases in susceptibility to toxins can occur when metabolic rates elevated by warmer temperatures increase uptake of pollutants.…”

Effects of insecticides on aquatic ecosystems in Bangladesh

“…However, earlier studies reported 10-d LC50 of chlorpyrifos for Chironomus tentans of 9956 µg/kg OC (Ankley et al, 1994) and for Chironomus dilutus of 10,800 µg/kg OC (Harwood et al, 2009), which is almost two times higher than our study (4500 µg/kg OC).…”

Inter-compartmental transport of organophosphate and pyrethroid pesticides in South China: Implications for a regional risk assessment

“…Chlorpyrifos water concentration reached a peak level of 8.36 ng/L assuming no air-to-water gaseous exchange occurred, and this concentration was significantly lower than the 4-d water-only median lethal concentration for C. dilutus of 459 ng/L (Harwood et al, 2009). In total, the air to water to sediment transport of chlorpyrifos suggested that its dynamic transport would decrease human inhalation exposure risk, but had little influence on its aquatic toxicity.…”