Environmental Loading of Tributyltin from Drydocks and Ship Hulls

Environmental loading factors for tributyltin (TBT) were studied in Pearl Harbor, Hawaii, between 1987 and 1988. During this period three test ships were painted with TBT-containing antifouling paint. The drydocks used to paint the vessels were monitored for overspray and discharges to both the harbor and the sewer system. Use of extensive dry-dock cleanup procedures, including masking 50% of the drydock floor, resulted in discharges to the harbor of <15 g TBT. Harbor concentrations were largely unaffected by TBT discharges of <3–149 ng 1-1 from the drydocks. Cleanup procedures were found to be successful in removing at least 99.8% of the residual paint overspray from the dry-docks, thus eliminating environmentally significant discharges to the receiving waters.The TBT flux from underwater hull coatings was evaluated by a device for measuring in-situ release rates, which documented order-of-magnitude differences (0.1–2.8 μg cm-2 d-1) in release rates among types of coatings. Tributyltin loading from the test ship hulls, ranging from 2 to 115 g d-1, generally covaried in a linear fashion with regional mean concentrations of TBT in the water column. An empirically derived model was used to predict future water column concentrations of TBT in Pearl Harbor of <10 ng 1-1 from Navy use, assuming application of low-release-rate (<2.0 (μg cm-2 d-1) paints and effective drydock cleanup procedures.