Effects of Chlorpyrifos on Individuals and Populations of Daphnia Pulex in the Laboratory and Field

Abstract

Abstract-Effects of the insecticide chlorpyrifos (cpf) on young (Ͻ1 d old) and adult (7-9 d old) Daphnia pulex and the ability of D. pulex to recover after exposure were tested in the laboratory. Populations of D. pulex exposed to cpf were studied in the laboratory and field. In the field, cpf was applied in a single dose. The effects of that dose on D. pulex populations were tested and compared with the effects of a simulated single dose and its ensuing decay on populations in the laboratory. The lowest no-observed-effect concentration was about 0.05 g/L (actual concentration). Chlorpyrifos immobilized D. pulex several days before death. Juveniles became immobilized faster than adults. Even when no longer exposed, D. pulex immobilized by cpf died. In the laboratory and field, observed population dynamics and effects of cpf on these dynamics were very similar. The median effective concentration for population size after 2 and 7 d of exposure did not differ between the laboratory and field (2 d, 0.38 and 0.31 g/L, respectively; 7 d, 0.25 and 0.34 g/L, respectively). Effects of cpf on single-species Daphnia populations in the laboratory and field can be predicted from effects observed in tests with individuals.

Cholinesterase and glutathione‐S‐transferase activities in freshwater invertebrates as biomarkers to assess pesticide contamination

“…Environmental risk assessment of pesticides for aquatic ecosystems is mostly based on the effects of individual compounds using single-species toxicity tests conducted either under controlled laboratory conditions or in the field [74][75][76]. While the value of these tests is incontestable in establishing safety standards for species protection, their wider ecological relevance has been questioned in recent years.…”

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

“…Induced individual tolerance from previous pulses may strengthen survivors (making them more tolerant [6]) through acclimation, induction of detoxification or biotransformation enzymes, and so on (e.g., induction of cytochrome P450—dependent mono‐oxygenases [7] and mixed‐function oxygenases in fish [8,9]). Cumulative individual effects occur when the first pulse weakens the organism (making it less tolerant), dissipating energy and lowering organism fitness [6], or the substance irreversibly interacts with the receptor [10,11]. Postexposure, latent, or delayed effects occur after a typical study is terminated.…”

“…Van der Hoeven and Gerritsen [10] studied the effect of chlorpyrifos on Daphnia pulex , reporting that the agrochemical immobilized daphnids several days before death. Even when exposure was discontinued, immobilized D. pulex died, further supporting the concept of irreversible effects.…”

Diazinon and chlorpyrifos in urban waterways in Northern California, USA

“…In general, a relationship between measured concentrations, results of toxicity tests, and receiving water effects has not been established with organophosphorous pesticides. However, in a recent study with chlorpyrifos and Daphnia pulex , the authors concluded that concentrations associated with effects in the laboratory were very similar to those that produced effects under field conditions [23]. Establishing such a relationship is unlikely to be possible in urban streams that are subject to a variety of contaminants and habitat alterations.…”