Spatial and seasonal behaviour of organotin compounds in protected subtropical estuarine ecosystems in Okinawa, Japan

Abstract

The spatial and temporal behaviours of the organotin compounds (OTCs) (butyl- and phenyltin) were investigated in the Manko and Okukubi protected estuarine ecosystems on Okinawa Island, Japan from February to October 2006. Butyltin compounds (BTCs) were frequently detected in all seasons, while phenyltin (PhTs) were found in winter and early spring. In Manko estuary, the total mean concentrations of BTCs and PhTs were 22.78 ± 30.85, (mean ± SD, n = 53) and 0.08 ± 0.27 ng(Sn) L−1, respectively. In Okukubi estuary, BTCs and PhTs were 12.58 ± 23.96 and 0.47 ± 1.67 (n = 55) ng(Sn) L−1, respectively. The Manko sediments can be classified as lightly contaminated, while the Okukubi sediments were uncontaminated with tributyltin (TBT). The mean levels of TBT shown in Manko estuary exceeded the threshold level and represent an ecotoxicological risk to sensitive aquatic life. Generally, the present study reports the occurrence and continuous input of OTCs in the protected estuaries, even 16 years after legal restriction of TBT usage in coastal waters was implemented by the Japanese Environmental Authorities.