Joint Acute Toxicity of Diazinon and Chlorpyrifos to Ceriodaphnia Dubia

Abstract

Abstract-Diazinon and chlorpyrifos are two organophosphorous pesticides widely found in municipal, agricultural, and urban storm water discharges. Because they are often found concurrently, their relationship with respect to joint toxicity is of interest, particularly in regard to interpreting the results of toxicity identification evaluations (TIEs) that point to metabolically activated organophosphorous pesticide(s) as causes of toxicity. Joint toxicity was evaluated using static tests that incorporated 48-to 96-h exposure periods using laboratory water, natural water, and urban storm water. Chemical concentrations were verified analytically. Mortalities were measured at 24-h intervals and joint toxicity was calculated on the basis of toxic units (TUs) for every time interval (1 TU ϭ median lethal concentration [LC50]). Forty-eight-hour LC50 values ranged between 0.26 and 0.58 g/L for diazinon and between 0.058 and 0.079 g/L for chlorpyrifos. The 96-h values were approximately 65% of their respective 48-h values. Under the assumption of strict additivity, the LC50 (as TUs) of the mixture should be the sum of the respective fractions of diazinon and chlorpyrifos and should total unity. These values were calculated for a total of 12 time intervals. The TUs associated with the mixtures in laboratory water ranged between 0.89 and 1.46, with an average of 1.13. The values for the natural and storm water samples were similar to those obtained with laboratory water. These data confirmed the results of TIEs that suggested that diazinon and chlorpyrifos exhibit additive toxicity when present together.

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

“…Additivity has been observed in C. tentans exposed to binary mixtures of the OPs chlorpyrifos, methidation, diazinon, and azinphos methyl [84] and for Ceriodaphnia dubia exposed to the OPs chlorpyrifos and diazinon [85], however, no enzymes measurements were performed in these studies. In contrast, Woods et al [86] observed synergistic effects between chlorpyrifos and profenofos tested on Ceriodaphnia dubia, attributed to an increase in the rate of enzymatic activation of one compound by the other or an inhibition of the enzymes that control detoxification.…”

A Probabilistic Screening Model for Evaluating Pyrethroid Surface Water Monitoring Data

“…The acute toxicity of diazinon and chlorpyrifos to C. dubia is additive (Bailey et al, 1997). Joint toxicity is estimated from diazinon and chlorpyrifos analytical data by normalizing each concentration to its respective LC 50 .…”

The Role of Traditional and Novel Toxicity Test Methods in Assessing Stormwater and Sediment Contamination

“…Pesticide pulses have been followed through watersheds, remaining toxic for days from agricultural runoff (Kuivila and Foe, 1995;Werner et al, 2000). Diazinon has been implicated as the primary toxicant in runoff causing acute toxicity to C. dubia, P. promelas, and in situ Corbicula fluminea assays (Bailey et al, 1997;Kuivila and Foe, 1995;Connor, 1995;Waller et al, 1995;Cooke et al, 1995). C. dubia reproduction and growth of C. fluminea in situ closely paralleled the health of the indigenous communities (Dickson et al, 1992;Waller et al, 1995).…”

“…In another study, stormwater (from large parking areas surrounding an airport and industry) toxicity was most strongly influenced by cationic metals. Diazinon and chlorpyrifos in urban stromwater showed additive toxicity to C. dubia in a TIE (Bailey et al, 1997). Jirik et al (1998) also used selected phase 1 TIE studies to identify the toxicants most responsible for stormwater toxicity in the Santa Monica Bay area.…”