The use of ecotoxicological risk assessment in deriving maximum acceptable half‐lives of pesticides

Abstract

Approaches in ecological risk assessment are usually based on estimating the probability that organisms will be exposed to environmental concentrations of chemicals greater than some toxicological criterion (LC50, NOEC). Following this approach, quality standards for persistent chemicals in soil can be derived. For readily degradable chemicals emitted at intervals, the ecological risk can be related to the time taken for the chemical concentration to fall to a level causing no effect on most, e.g. 95%, of the species. A formula is derived for the maximum acceptable half‐life, assuming a log–logistic distribution of species susceptibilities and a simple exponential decay of the chemical. It is also assumed that the pesticide is distributed homogeneously through the top 20 cm of the soil. A numerical example is elaborated for carbofuran, demonstrating that for a recommended dose applied to soil, the maximum half‐life should be 47 days, if the ecotoxicological protection level is to be reached within one year after a single application. This estimate may vary between 35 and 61 days, depending on the margins of uncertainty attached to ecotoxicological data. Complete recovery not only includes the disappearance of the chemical but also the recolonization of treated soils. The half‐life condition derived in this paper should therefore be considered as a minimum requirement.

Higher‐tier laboratory methods for assessing the aquatic toxicity of pesticides

“…One approach to predict the likely recovery of a system is based on the dissipation half‐life of the compound, the initial exposure concentration and the hazardous concentration for 5% of species 65. If recovery is required within a year after a single application, then the chemical's half‐life should meet the condition: where T 1/2 is measured in years, C 0 is the initial concentration and HC 5 is the hazardous concentration for 5% of species.…”

Temperature–Time Relationship in Collembolan Response to Chemical Exposure

“…Reproduction rate is an especially important parameter for a species that allocates a great amount of resources to reproduction (van Straalen et al, 1992). Collembolans are an example of a species group that usually has high fecundity.…”

Open Problems in the Derivation of Soil Quality Criteria from Ecotoxicity Experiments

“…Van Rijn et al (1993) and Van Straalen et al (1992) have suggested a simple model to incorporate the above mentioned arguments in an ecotoxicological risk assessment for pesticides in soil. Degradation of the toxicant is assumed to follow a simple exponential decay process, characterized by a half-life DT50 (in days).…”