Biological Effects of Continuous and Intermittent Dosing of Outdoor Experimental Streams with Chlorpyrifos

Abstract

Two outdoor experimental streams fed by water pumped from the Mississippi River were dosed with the organophosphorus pesticide chlorpyrifos (the active ingredient of Dursban® and Lorsban 4E® insecticides) for 100 days, and the responses of individual species and communities compared to those of a control stream. Chlorpyrifos was continuously metered into one stream whereas the other received 8 biweekly additions, each lasting 24 h, at 14 times the concentration in the continuously dosed stream. Therefore, nearly equal amounts of pesticide were introduced into each stream during the experiment. The biological study area of each stream was approximately 245 m long, contained a naturally colonizing plant and invertebrate assemblage, and was stocked with fathead minnows and bluegills. Measured system characteristics included macroinvertebrate drift and riffle benthos composition; fish survival, growth, reproduction, food habits, tissue residues, and AChE inhibition; and system functional process indicators (P/R ratios, biodegradation, nitrate and dissolved organic carbon [DOC] concentrations, and bacterial growth and heterotrophic activity). The macroinvertebrate communities reacted similarly in the continuously and pulse-dosed streams. Species diversity decreased by equal amounts and was still decreasing at the end of the test. Crippling of fathead minnows and reversible acute toxicity symptoms (lethargy, tetany when startled) in bluegills were observed only in the pulse-dosed stream. Fish survived, reproduced, and grew equally well in all streams. There seemed to be good agreement between laboratory and field effect concentrations for fish and invertebrates. Functional process indices, with the possible exception of biodegradation, appeared unaffected and considerably less sensitive than other characteristics measured. The results of the project are discussed in relation to lab to field extrapolation and the need for further testing.

Ecotoxicology of Chlorpyrifos

“…Brain AChE inhibition in fish from treated streams ranged from 41070 to 93% of control levels. System functional responses (i.e., production/respiration, organic matter mineralization, organic carbon production, microbial biomass production, heterotrophic activity) were not affected, but plant tissue decomposition may have been reduced (Eaton et al 1985). Pulseyet al (1994) evaluated the effects of a single pulse dose of chlorpyrifos (6-hr exposure at mean measured concentrations of 0.06 or 2.6 p.g/ L) in artificial stream systems (Queensland, Australia).…”

“…The abundance of mayflies, caddisflies, and blackflies in the treated stream areas returned to pretreatment levels within 30 d of chlorpyrifos application, but stonefly abundance remained reduced (Wallace et al 1973). Eaton et al (1985) evaluated the ecological effects of continuous (0.22 p.g/L nominal; average measured concentration ranged from 0.12-0.83 p.g/ L) and intermittent (3.1 p.g/L nominal; average estimated pulse concentration ranged from 0.94-7 p.g/L) chlorpyrifos exposure in experimental streams (Minnesota, U.S.) for 100 d. The intermittent application consisted of eight biweekly treatments metered to provide the same approximate total exposure as administered to the continuously exposed stream. The top predators in the system were fish: fathead minnows, bluegill, and white suckers.…”

“…Aquatic communities in both intermittently and continuously exposed streams responded similarly, except that fish in the intermittently dosed stream exhibited increased spinal deformities (fathead minnows) and transient lethargy or tetany (bluegill). Also, the predominant macroinvertebrates shifted from amphipods to isopods in the continuously dosed stream (Eaton et al 1985). Macroinvertebrate communities exhibited reduced species diversity, but total abundance was not affected.…”

“…There were no apparent adverse effects on fish survival, growth, or reproduction. Apparent BCFs in fish ranged from 100 to 780 (Eaton et al 1985). Brain AChE inhibition in fish from treated streams ranged from 41070 to 93% of control levels.…”

Evaluation of evidence that the organophosphorus insecticide chlorpyrifos is a potential persistent organic pollutant (POP) or persistent, bioaccumulative, and toxic (PBT)

“…Empirical values for BCFs for fish ranged from 0.6 to 5,100 [79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94] (see Additional file 1: Table S5A). From the distribution, the smallest value was clearly an outlier and was omitted from the calculation of the geometric mean and the regression.…”