Availability and toxicity of pendimethalin to aquatic microorganisms

Abstract

The characterization of bioavailability and toxicity of pesticides is necessary for the assessment of environmental risk caused by these chemicals. Pendimethalin is a dinitroaniline herbicide used for selective control of most annual grasses and many annual broad-leaved weeds in several crops. The technical formulation of this herbicide, Stomp 330, has been approved in Lithuania and is applied to winter rye, barley, maize, winter wheat, as well as to some vegetable crops. The objective of this study was 1) to evaluate the bioavailability and toxicity of pendimethalin to three species of aquatic microorganisms: green microalgae Selenastrum capricornutum, ciliate protozoa Tetrahymena thermophila and luminescent bacteria Vibrio fischeri; 2) to compare the toxicity of pendimethalin-standard (pure compound) and technical formulation of herbicide Stomp 330 to the microorganisms tested. The growth of algae S. Capricornutum was most sensitive to pendimethalin (the value of EC50 for pendimethalinstandard – 52 g/l) In the tests with T. thermophila and V. fischeri, the values of EC50 for pendimethalin were above the water solubility level of this compound (0.3 mg/l). The effect of Stomp 330 on bacterial bioluminescence appeared in a shorter time as compared to the effect of pure pendimethalin. The difficulty in evaluating the bioavailability and toxicity of poorly watersoluble substances to microbial cells is discussed. Keywords: pendimethalin, Stomp, bioavailability, toxicity, bacterial bioluminescence