Toxicity and Reproductive Effect of Combination Pesticide to Daphnia magna

Abstract

Daphnia magna is ubiquitous link in ecological food chain; they are small planktonic crustacean used in ecotoxicological acute tests and chronic reproduction studies. Daphnia species are very sensitive to xenobiotics and very low concentrations will affect their survival. The objective is to investigate the toxicity and reproductive effect of Daphnia magna exposed to different concentrations of combination pesticide in M4 medium in accordance to OECD 211 guideline and in exposure water. To maintain the water hardness within the range in the exposure water as per the OECD guideline reverse osmosis water and drinking well water was blended 1:1 ratio. Twenty one days semi-static exposure was conducted with 10 daphnia held individually in each treatment and control. Daphnids were exposed to 0.0000134, 0.000134, 0.00134, 0.0134, 0.134, 1.34 and 13.4 µg/L of Chlorpyrifos 50% + Cypermethrin 5% EC. 10 µL of alga and yeast were fed with for daphnia of water and only alga was provided M4 medium during the semi-static 48 hour medium change. Agilent QQQ GC-MS/MS, Election Impact Ionization mode was used for active content analysis. Stock solution of 13.4 µg/L was analyzed for its active content chlorpyrifos and cypermethrin. At 0 hour it was 89.7%, 87.5% and at 48 hour it was 85.3%, 72.4%, respectively. 0.0000134 µg/L was below limit of quantification level. Statistical analysis was performed with ECOSTATS program version 2012.06.03 (SAS Version 9.3, SAS Institute Inc., Cary, NC, USA, 2002-2010). EC50 calculated was 0.012 µg/L for M4 medium and 0.003 µg/L for exposure water at the end of 21 days. Parental mortality of daphnia and reproduction rate decline of off-springs collected in M4 medium and exposure water was found to be dose dependent. Significant change (P < 0.05) in off-spring reproduction was observed in M4 medium and exposure water by ANOVA Student-Newman-Keuls test. Based on the EC50 it is concluded that the pesticide is toxic to daphnids exposed in water than M4 medium exposure. Pesticide mixture effects and its interactions within mixtures is an area of concern to public and regulatory authorities, hence the combined actions of pesticides need to be addressed in the risk assessment process since mixtures of these chemicals may cause higher toxicity effects than those expected from the single compounds. Endocrine disrupting chemicals are compounds that alter the normal functioning of the endocrine system of both wildlife and humans and the tested pesticide active ingredient is considered as endocrine disruptor; no reliable data is available on the reproduction effect of the combination pesticide and this experiment throws light that exposure water can also be used to assess contamination of pesticide like M4 medium which is used regularly in ecotoxicological studies for pesticide toxicity assessment