Toxicity of Atrazine and Molinate to the Cladoceran Daphnia carinata and the Effect of River Water and Bottom Sediment on Their Bioavailability

Atrazine and molinate are widely used herbicides and concern has been raised about their potential deleterious impacts on aquatic ecosystems. Although there have been some studies on the toxicity of herbicides to aquatic organisms using laboratory or natural water, information on the effect of sediments, suspended particulates, and dissolved organic matter on their bioavailability is quite limited. This study aims to provide toxicity data that considers these factors and the effect that these factors have on bioavailability. In this study, the toxicity of the test chemicals was calculated following the Organisation for Economic Co-operation and Development (OECD) methods, whereas change in bioavailability was measured using EC 50 values based on measured initial concentrations of the test chemicals. The acute (48-h) static toxicity of atrazine and molinate to the freshwater cladoceran Daphnia carinata was determined in cladoceran water and river water in the absence and presence of sediment. The 48-h EC50 (immobilization) values of atrazine to D. carinata ranged from 22.4 to 26.7 mg/L, while the corresponding values for molinate ranged from 18.3 to 33.6 mg/L, respectively. Both chemicals were classed as having low acute toxicity to D. carinata. The presence of dissolved organic matter and suspended particles in river water did not significantly (p > 0.05) reduce the bioavailability (measured as toxicity) of atrazine to D. carinata compared to that tested in cladoceran water. The presence of sediment, however, significantly (p < 0.05) reduced the bioavailability (48-h EC50) of atrazine in cladoceran water, from 24.6 to 30.7 mg/L, and in river water, from 22.4 to 31.0 mg/L. Similarly, the presence of sediment in cladoceran water, significantly (p < 0.05) reduced the bioavailability (48-h EC50) of molinate, from 26.6 to 46.4 mg/L, and in river water, from 22.5 to 45.6 mg/L

Toxicity and bioavailability of atrazine and molinate to the freshwater shrimp (Paratya australiensis) under laboratory and simulated field conditions

Acute (96-h) semistatic toxicity tests were conducted by exposing the freshwater shrimp, Paratya australiensis, to atrazine and molinate in laboratory water and in river water both with and without sediment. The median lethal concentrations (LC50) and 95% fiducial limits of atrazine for P. australiensis in laboratory water in the absence and presence of sediment were 9.9 (8.6-11.5) and 6.8 (5.4-8.5) mg/L, respectively, while the corresponding values in river water were 9.8 (8.5-11.2) and 6.5 (5.4-7.8) mg/L, respectively. For molinate, the LC50 values in laboratory water in the absence and presence of sediment were 9.2 (7.0-12.1) and 9.0 (6.8-12.0) mg/L, respectively and the corresponding values in river water were 8.7 (6.4-11.8) and 8.2 (6.6-10.2) mg/L, respectively. Neither the river water nor the presence of sediment significantly (P<0.05) reduced the bioavailability of either chemical to P. australiensis. This was unexpected, as studies with other aquatic organisms have shown that sediment significantly reduced the bioavailability of these chemicals. © 2004 Elsevier Inc. All rights reserved

The toxicity and bioavailability of atrazine and molinate to Chironomus tepperi larvae in laboratory and river water in the presence and absence of sediment

Acute (10 day) semi-static toxicity tests in which the midge, Chironomus tepperi, were exposed to atrazine and molinate were conducted in laboratory water and in river water, in the absence and presence of sediment. The bioavailability measured as median lethal concentrations (LC50) and 95% fiducial limits (FLs) of atrazine to C. tepperi in laboratory water in the absence and presence of sediment were 16.6 (14.3-19.4) and 21.0 (18.2-24.1) mg l-1, respectively while the corresponding values in river water were 16.7 (14.7-19.0) and 22.7 (20.3-25.4) mg l-1, respectively. For molinate, the LC50 and FL values in laboratory water in the absence and presence of sediment were 8.8 (6.8-11.4) and 14.3 (12.4-16.4) mg l -1, respectively and the corresponding values in river water were 9.3 (7.6-11.3) and 14.5 (12.4-16.9) mg l-1, respectively. Atrazine has low toxicity (LC50 > 10 mg l-1) while molinate has moderate toxicity (1 mg l-1 0.05) reduce the bioavailability of either chemical to C. tepperi. However, the presence of sediment did significantly (P < 0.05) reduce the bioavailability of both atrazine and molinate to C. tepperi. © 2004 Elsevier Ltd. All rights reserved

Assessing the chronic toxicity of atrazine, permethrin, and chlorothalonil to the cladoceran Ceriodaphnia cf. dubia in laboratory and natural river water

The majority of ecotoxicological data are generated from standard laboratory-based experiments with organisms exposed in nonflowing systems using highly purified water, which contains very low amounts of dissolved organic matter and suspended particulates. However, such experimental conditions are not ecologically relevant. Thus, there is a need to develop more realistic approaches to determining toxicity, including both lethal and sublethal effects. This research provides information on the effect of natural water constituents, such as suspended particulates and dissolved organic matter, in river water (RW) on the chronic toxicity (7-day reproductive impairment) of the pesticides atrazine, chlorothalonil, and permethrin to the freshwater cladoceran Ceriodaphnia cf. dubia. Standard bioassays were conducted under standard laboratory and more environmentally realistic conditions (using RW). The 7-day IC25 (reproduction impairment) values of atrazine, chlorothalonil, and permethrin to C. cf. dubia ranged from 862.4 to >1000, 51.3 to 66.4, and 0.19 to 0.23 μg/L, respectively. Using the Globally Harmonized System of Classification and Labelling of Chemicals, atrazine is classified as moderately to highly toxic, whereas permethrin and chlorothalonil were both highly toxic. The presence of dissolved organic matter and suspended particles in natural RW did not significantly (p > 0.05) change the toxicity of any of the pesticides to C. cf. dubia compared with that tested in laboratory water (LW). For the tested pesticides, toxicity testing in LW provided an adequate estimate of the hazard posed. © 2012 Springer Science+Business Media New York