Effects of organochlorine pesticides (OCPs) on survival and edibility of loaches in the World Heritage Honghe Hani Rice Terraces, China

Abstract

A new rice-loach co-culture system was introduced into the Honghe Hani Rice Terraces (HHRT), China, to promote sustainable development of this World Heritage region. However, little is known about the survival of loaches in this area and whether they are safe to eat after having been exposed to residual organochlorine pesticides (OCPs). Although some OCPs such as dichlorodiphenyl trichloroethanes (DDTs), hexachlorocyclohexanes (HCHs), aldrin, and dieldrin have been banned in China, they can still be detected in the agricultural environment. In this study, water, sediment, and loaches (water and sediment collected 3 times; loaches only at harvest) in the HHRT were simultaneously sampled throughout the culture season and analyzed for 22 selected OCPs. Results showed that the concentration of total OCPs in the water and sediment uniformly decreased in the following order May > August > October and that samples collected during August and October clustered together in nMDS analysis, differing from those collected in May. Some OCPs, such as heptachlor, heptachlor epoxide, endosulfan I, endosulfan II, DDTs and HCHs were present in abundance. DDTs and HCHs were persistently present in low sediment concentrations at 0.21-1.27 and 0.01-0.95 µg kg-1, respectively, suggesting that a new origin of these pesticides may exist. Heptachlor accounted for the majority of OCPs at the beginning of the co-culture season and was calculated to influence the survival of loaches. Residual OCPs were generally not detected in the muscle of loaches (i.e. the edible part of loaches) being sent to market and therefore pose a low risk to humans who eat them. Overall, the results of this study will be useful in the production and consumption of loaches in rice-loach co-culture systems, as well as for the promotion of sustainable development of the HHRT.