Altered Serum Levels of Sex Steroids and Biotransformation Enzyme Activities by Long-term Alachlor Exposure in Crucian Carp (Carassius auratus)

Abstract

In the past several decades, a variety of environmental chemicals such as pesticides have been found to be responsible for detrimental reproductive effects in wildlife and human. These compounds, termed as endocrine disruptors (EDs), can alter endocrine function and subsequently may disrupt growth, development and reproduction (Colborn et al. 1993). Alachlor (Fig. 1) [2-chloro-N-(2, 6-diethyl phenyl)-N-(methoxymethyl) acetamide] is a commercialized effective pre-emergence and post-emergence herbicide in control of most grasses, most annuals and some broad leaved plants (Hayes and Laws 1991). It is a selective systemic herbicide, absorbed by germinating shoots and roots, works by interfering with the ability of plant to produce protein and by interfering with root elongation process. It has been used in the United States, Europe, Asia and other places in the world (Donaldson et al. 2002). Because of its widespread use, alachlor has been found in both surface water and groundwater in different countries (Barcelo et al. 1996; Spalding et al. 2003). And the presence of alachlor in freshwater is likely to pose health hazards to non-target aquatic organisms and human (Chesters et al. 1989). Therefore, the aquatic ecological risk from this herbicide becomes an important worldwide concern (Gammon et al. 2005). Alachlor is classified as the carcinogen of B2 group and known as a highly toxic EDs (USEPA 1985). The potential toxicity of alachlor has been studied in a series of rodent chronic bioassays in mouse, rat, monkey, and isolated hepatocytes (Bonfant et al. 1992; Meisner et al. 1992). However, there has been a limited investigation of its endocrine disrupting effect in fish, which may be directly affected by this herbicide as they live in the surrounding aquatic environment near farmland. So far, only few studies have yet been performed by using crucian carp as an environmentally sensitive freshwater species. The aim of this study is to investigate the endocrine disrupting effect including perturbation of the endocrine parameters and phase II biotransformation enzymes activities in response to long-term alachlor exposure. The serum hormonal levels of serum sex steroids (testosterone and 17b-estradiol) and activities of hepatic microsome enzymes (glutathione S-transferase (GST) and UDP-glucuronosyltransferase (UDPGT) are evaluated. The relationship between the levels of serum sex steroids and hepatic microsome enzyme activities is discussed.