Effects analysis of time‐varying or repeated exposures in aquatic ecological risk assessment of agrochemicals

Abstract

Exposure to agrochemicals in the aquatic environment often occurs as time-varying or repeated pulses. Time-varying exposures may occur due to runoff events and spray drift associated with precipitation and application events. Hydrologic dilution, dispersion, and degradation also produce pulsed exposures. Standard laboratory toxicity tests using constant exposure concentrations typically do not investigate the toxicity of time-varying or repeated exposures. Detoxification, elimination, and recovery may occur within organisms or populations during the periods between exposures. The difficulty of estimating effects of realistic time-varying exposures from measurements made under constant exposure conditions is often an important source of uncertainty in ecological risk assessment of pesticides. This article discusses the criteria and tools for deciding whether time-varying exposures are relevant in a particular risk assessment, approaches for laboratory toxicity testing with time-varying exposure, modeling approaches for addressing effects oftime-varying exposure, deterministic and probabilistic ecological risk characterization of time-varyingexposures and toxicity, and uncertainty analysis.

Making Sense of Ecotoxicological Test Results: Towards Application of Process-based Models

“…In the European guidelines (EC, 2003), the local scenarios encounter this problem for non-continuous emissions: surface water concentrations of pollutants are high during the emission episode, but low outside that period. For pesticides, pulsed exposures are even more common and model approaches to predict effects are required (Reinert et al, 2002).…”

“…However, the data can still be used in a process-based model (Péry et al, 2001). When concentrations decrease in time, additional assumptions may be needed about the recovery of the organisms (Reinert et al, 2002). Similarly, mechanistic models allow dealing with ionizing compounds (Kooijman, 2000), growing organisms (Kooijman and Bedaux, 1996a), or a decline in body weight in the test.…”

Effect of Sequential Isoproturon Pulse Exposure on Scenedesmus vacuolatus

“…As reviewed by Reinert et al (2002), the long-term effects on nontarget organisms of fluctuating pesticide exposure can be a function of the damage sustained during exposure, the capacity of the organisms to recover, and the duration of the recovery period between pulses. Furthermore, sequential exposure to pesticides could lead to an increased or a decreased effect during each subsequent exposure, depending on the organisms tested and the mode of action of the chemical.…”

Environmental Risk Assessment of Heavy Metals of Road Runoff in Ehimiri Housing Estate Umuahia, Abia State, Nigeria

“…Standard laboratory toxicity tests usually used to assess the effects of pollutants utilize continuous exposure scenarios and typically do not investigate the toxicity of short-term pulsed or intermittent exposures to aquatic organisms. In fact, the necessity in assessing the effects of such high concentrations events have been discussed by several authors Reinert et al 2002;.the study therefore seeks to assess the impact of run off on the quality of the Ehimiri river because of its usefulness to the people of the area who use it for domestic, industrial and agricultural purposes.…”