An assessment of the association of organochlorine pesticide contamination and reproductive effects on the snail-eating turtle (Malayemys Macrocephala) in the lower Chao Phraya River Basin, Thailand

Abstract

Organochlorine pesticides (OCPs) are persistent and bioaccumulative toxicants that may cause reproductive impairments in wildlife as well as human. It is thus important to examine the extent of contamination and the potential reproductive effects on the animals living in area with history of OCP uses. In this study, the snail-eating turtle (Malayemys macrocephala) is used as a sentinel for OCP contamination in the Chao Phraya River Basin because it is a long-lived vertebrate with a home range overlapping a potentially affected area. Study on nesting and reproductive biology showed that M. macrocephala has clutch size of 3-10 eggs, egg size of 22 x 38 mm and egg weight of 11.6 g. Egg incubation in a temperature-controlled incubator resulted in incubation period of 82-186 days with hatching success of 36-54%. A novel non-invasive sexing technique has been developed based on a morphometric study and can be used to predict sex of juvenile turtle with an accuracy of 85.3%. Incubation at different temperatures resulted in different sex ratio suggesting that M. macrocephala has temperature-dependent sex determination. Analyses for OCP residues in nest soil, female blood and complete clutch of eggs revealed detectable levels in nest soil and turtle eggs. OCP residue analysis in eggs showed that 5 groups of OCPs (HCHs, chlordanes, DDTs, endosulfans, and aldrin and dieldrin) were detected in turtle eggs, and HCHs was the most predominant residues. Egg incubation at 29 ℃ revealed the hatching success of 66.95% and the neonate survival rate of 92.40%. Although no correlation between OCP levels and survival rate was found, the levels of Σchlordane in eggs were positively correlated with percentage of hatchling that requires assistance after egg pipping in order to emerge from eggshell. Levels of ∑HCH in eggs were found to associate with an increased incidence of deformities in M. macrocephala. Levels of OCP residue in eggs were also found to skew the sex ratio toward male-biased ratio. Overall, the results indicated that, although OCPs had been banned, their low level contamination is still present in central agricultural plain of Thailand. Associations between OCP residues and hatching success, deformities and sex ratio of the turtles suggest the potential ecological risk of OCP contamination on reproductive health and population status of the long-lived vertebrate living in area with history of OCP utilization.