Appendix 2 Open Literature Review Summaries for Malathion
Description of Use in Document
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Description of Use in Document: Valid for arrays (qualitative). Rationale for Use: Study appears to be of sufficient quality to characterize behavioral effects (swimming) after exposure to malathion. Limitations of Study: A negative control group was not used, with the test only containing a solvent control. Test solutions were not measured, nominal concentrations were used. It is noted that the behavioral responses regarding recovery did not exhibit a concentration response as the fish in the lower concentration took longer to show signs of recovery compared to the higher treatment. Primary Reviewer: Amy Blankinship, Chemist, EBR6 Secondary Reviewer: Elizabeth Donovan, Biologist, ERB6 Open Literature Review Summary Chemical Name: Malathion, PC Code: 057701(malathion) ECOTOX Record Number and Citation: 62046. Belden JB, Lydy MJ. 2000. Effects of Atrazine on Acetylcholinesterase Activity in Midges (Chironomus tentans) Exposed to Organophosphorus Insecticides. Chemosphere 44(8): 1685-1689 Purpose of Review: Endangered Species Assessment. Date of Review: November 29, 2016. Summary of Study Findings: While malathion and chlorpyrifos and methyl parathion were tested in this study, this review focuses on malathion. Methods Forth instar Chironomus tentans larvae (confirmed based on head capsule width and cultured from eggs masses obtained from Environmental Research Laboratory in Duluth Minnesota) were exposed to atrazine-treated water or solvent control for 24 hours. Subsequently, the midges were exposed to either an OP or OP+atrazine (200 µg/L) for 24 hours. Test methods were previously reported in Belden and Lydy, 2000, and consisted of 1L beakers containing 3mm silica substrate and 1L of moderately hard reconstituted water. Based on Belden and Lydy, 2000, it was assumed that the beakers were kept at 20°C and 16:8 light:dark cycle, and temperature, dissolved oxygen, pH and conductivity were monitored before and after each test. Each beaker contained 10 larvae and 5 replicates were used per treatment. The chemicals were delivered to the water using 100 µL of acetone. Analytical-grade malathion was used in preparing the test solutions (≥98%, Cheminova, Lemvig, Denmark). The test concentrations for the OPs were based on EC01 or EC50 (previously conducted; Belden and Lydy, 2000) based on swimming behavior. After 24 hours of exposure, all midges within a single beaker were homogenized and acetylcholinesterase (AChE) activity was measured. Results AChE activity was significantly reduced when compared to the control at the EC50 concentration (1.5 µg/L), but not at the EC01 concentration (0.26 µg/L). The OP+atrazine group was not significantly different from the EC01 or EC50 group (Figure 1, copied without alteration). 
Description of Use in Document: Quantitative for behavioral line of evidence in ESA risk assessment. Rationale for Use: Study appears to be of sufficient quality to characterize AChE effects after exposure to malathion [given that the test material was provided by Cheminova, the reviewer assumed that the impurity profile is known and within current limits]. Limitations of Study: A negative control group was not used, with the test only containing a solvent control. Test solutions were not measured, nominal concentrations were used. The survival rate of the control and treatment groups were not reported. Primary Reviewer: Amy Blankinship, Chemist, EBR6 Secondary Reviewer: Reference: 56553. Belden JB, Lydy MJ. 2000. Impact of Atrazine on Organophosphate Insecticide Toxicity. Environ. Toxicol. Chem. 19(9): 2266-2274 Open Literature Review Summary Chemical Name: Malathion, PC Code: 057701(malathion) ECOTOX Record Number and Citation: 56553. Belden JB, Lydy MJ. 2000. Impact of Atrazine on Organophosphate Insecticide Toxicity. Environ. Toxicol. Chem. 19(9): 2266-2274 Purpose of Review: Endangered Species Assessment. Date of Review: November 29, 2016. Summary of Study Findings: While malathion, diazinon, chlorpyrifos and methyl parathion were tested in this study, this review focuses on malathion. Methods Forth instar Chironomus tentans larvae (confirmed based on head capsule width and cultured from eggs masses obtained from Environmental Research Laboratory in Duluth Minnesota) were exposed to either an OP or OP+atrazine (200 µg/L) for 96 hours. Solvent and negative controls were included. Tests were conducted in 1L beakers containing 3mm silica substrate and 1L of moderately hard reconstituted water. Each beaker contained 10 larvae and 3 replicates were used per treatment. The chemicals were delivered to the water using 50 µL of acetone. Analytical-grade malathion was used in preparing the test solutions (≥98%, Cheminova, Lemvig, Denmark). The endpoint measured was the effective concentration which represented the concentration where a percentage of the test population was unable to perform normal swimming motion when pinched with a pair of forceps. Preliminary tests were conducted using atrazine and each OP separately. The EC01, EC05, EC15 and EC50 were determined for each OP using probit. After the preliminary testing, a factorial test design was used in which the EC01, EC05, EC15 and EC50 concentration were combined with atrazine concentrations of 0, 10, 40, 100 and 200 µg/L were added. Test concentrations were measured using solid-phase extraction and analysis by gas chromatography with nitrogen phosphorus. The extraction efficiencies for malathion were reported as 95.7%±6.1. Uptake and oxygen consumption and in vivo/ in vitro biotransformation studies were conducted with chlorpyrifos and atrazine but are not summarized here. Results Temperature was maintained at 20±1°C and dissolved oxygen was >70% saturation. Conductivity was 320-350 µS/cm and pH ranged from 7.3-7.8. All initial water concentrations were within 10% of nominal and dropped to 74-84% for malathion at the end of the test. All results are based on nominal concentrations. The ECx values for each OP individually is presented below (Table 1, copied without alteration). The addition of atrazine did not significantly increase the toxicity of malathion. 
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