Study on the sensitivity of certified bioassays to water pollution with modern herbicides: Model experiments

Abstract

Introduction: Imidazolinone herbicides and pyridine derivatives are modern weed control products. Experts attribute the possibility of introducing into the soil and on plants, wide spectrum of action against undesirable plants, and protection of fields throughout the growing season to their advantages. Manufacturers claim the environmental friendliness of using the latest generation of herbicides due to their rapid destruction in the environment. But various studies have shown that the use of modern herbicides affects both microorganisms and large animals. Therefore, diagnostics of herbicide contamination in the soil and water bodies is an urgent task. Methods: We studied the effects of imidazolinones (imazetapir and imazamox) and pyridine derivatives (a mixture of clopyralid and picloram) on living organisms. Those substances are recommended for use in the Clearfield system. Commercial forms of preparations (aqueous solutions) were produced in the Russian Federation and the Republic of Belarus under the Rodimich (imazamox), Golf VK (imazetapir), Akteon (a mixture of clopyralid and picloram) trademarks. For the purposes of calculation, the following maximum allowable concentrations (MAC) in water were taken: for imazetapir — 0.01 mg/l, for clopyralid and picloram — 0.04 mg/l, for imazamox — 0.004 mg/l. The practical task was to determine the sensitivity of bioassays certified in Russia to this specific pollution. We compared the sensitivity of bioassays in terms of mortality of Daphnia magna and Ceriodadhnia affinis, Paramecium caudatum chemotaxis, and Escherichia coli bioluminescence changes. Additionally, we rated chronic effects for D. magna. Results: Crustaceans D. magna and C. affinis were not sensitive to the test substances. Death of C. affinis occurred in response to doses of 350 MAC, and for D. magna, supplements equal to 300 MAC were lethal. Experiments showed that the threat of herbicides to these aquatic organisms increased in the following series: imazetapi < < clopyralid + picloram < imazamox. The bioassays for the pre-lethal reactions of microorganisms P. caudatum and E. coli were more sensitive. A mixture of clopyralid and picloram inhibited the test functions of microorganisms in response to a minimum dose of 1 MAC (using clopyralid). The negative effect of imazetapir on ciliates started with 10 MAC, on E. coli — with 50 MAC. Imazamox was the safest. It had an effect only at a dose of 50 MAC. As for P. caudatum and Ecolum test system bacteria, the following series of risk increase regarding the active ingredients in preparations is valid: imazamox (Rodimich) < < imazetapir (Golf VK) < < clopyralid + picloram (Akteon). In chronic experiments with D. magna, it was shown that modern herbicides caused a delay in the maturation of females D. magna and later appearance of the young in comparison with the control (by 1–2 days). As a result, in 24 days of the experiment, the fertility of D. magna was significantly depressed in response to doses in the range from 1 to 50 MPC — by 1.3– 1.8 times (p < 0.05). Conclusion: The experiments showed that the sensitivity of the four bioassays for imazetapyr, imazamox, and the mixture of clopyralid + picloram could be represented by the following series: the bioassay for changes in chemotaxis of P. caudatum > the bioassay of bioluminescence reduction in E. coli > the bioassay for the mortality of C. affinis > the bioassay for the mortality of D. magna.