Monitoring Of Tributyltin In The Marine Environment

Abstract

Field investigations by our laboratory were designed to measure and compare regional differences in tributyttin loading for three major use categories: regions Of ecological importance such as fishing or nursery areas, regions containing commercial or recreational vessels such as marinas or vessel repair f a c i k s and regions near u-sNavy v e ~ ~ e l s ~ ~ t h o d s for WratOrY analysis during the^ studies have been described Previously (13)initial baseline studies and subsequent harbor monitoring investigations have consistently ShOwn that the highest tributybn loading Occurs near marinas and vessel repair facilities (2,4,5)In comparison, data from "far-field" regions, well-flushed areas away from b w w n sources, have shown low background TBT levels in the range Of 2-10 ng/L in most harbors studied. Tributyttin ~ B T ) compounds have been used as biocides in marine antifouling paint formulations since the late 1 ~ s . Recent concern about deleterious effects on non-target -ne organisms has resutted in legislation and regulation to reduce inputs of TBT into the aquatic environment. Accurate and welldesigned monitoring programs are required to determine both the necessity and efficacy of TBT environmental regulation. There have been numerous TBT baseline studies performed in France, the U K , Canada and the U.S., however, very few comprehensive monitoring programs have been conducted. From our work, which encompasses baseline measurements in fifteen U.S. harbors and intensive monitoring in three regions (Pearl Harbor, San Diego Bay and Norfolk), we have found the following: The principal sources and highest concentrations of TBT are in marinas, small boat harbors and in the vicinity of vessel repair facilies and berthing areas, with concentrations ranging from 10-1000 ng/L; regions of harbors and estuaries are generally below 10 ng/L; High variability in TBT concentrations can be caused by tidal effects, seasonal changes (e.g. intensity of pleasure vessel use, temperature, fresh-water input), vertical stratification of the water column, and intermittent point source discharges such as drydocks; Knowledge of TBT sources and degree of variability are important in designing and interpreting monitoring programs; and In general, sediment TBT concentrations are about three orders of magnitude greater than water concentrations while TBT levels in bivalve tissue (mussels and oysters) show bioconcentration factors ranging from 5,000 to 50.000. DISCUSSION Variable environmental factors such as tidal circulation patterns, vertical stratification of the water column and intermittent butyttin source discharges have been shown to affect Tributyttin concentrations in well-flushed open butyttin sampling results in certain harbors (1,7). In some estuaries such as Pearl Harbor, tidal effects and stratification have been shown to be less important to monitoring design considerations (5). The seasonal abundance of pleasure craft, especially in temperate regions, has a measurable effect on butyttin concentrations present in the water column (8,9,10) and should be considered during monitoring study design planning. A regional approach to butyttin characteriition within a specific harbor system offers a useful means to describe the results of environmental butyttin monitoring. By character-king butyttin concentrations of similar harbor regions, distinguishable patterns and trends have emerged from our monitoring studies. Marinas and vessel repair facilities have consistently provided the highest TBT concentrations. However, recent trends in TBT concentrations from these regions conducted after TBT restrictive use legislation may reflect a shift in use from TBT to copper-based paints among the small craft community. Surface water TBT measurements in marinas or near vessel repair facilities have generally been several-fold higher than Seen in samples taken from near-bottom Waters. increased sediment TBT concentrations were correlated with proximity to vessel mOorage and repair facilies and were generally about three orders of magnitude greater that surface water TBT W"tratiOnS. Mussel and Oyster tissue TBT levels were also highest near these source regions and showed bioconcentration faCtOrS ranging from 5,000 to 50,000 (1 1). Average butyttin values in surface water, sediment and tksue monitoring Samples collected over a three year period in four harbors, San Diego Bay, Pearl Harbor, Honolulu Harbor and the Norfolk Harbor are summarized in Table 1. Where results were below detection limits, values were reported as zero in the table. INTRODUCTION Few compounds introduced into the marine environment have provided such stimulation for fervent regulatory discussion and environmental research controversy as in the m e of butyhns. The concern for possible deleterious effects on nontarget marine biota has precipitated statutory regulation both within the U.S. and abroad. During the p m six years the Naval ocean systems Center has performed comprehensive field and laboratory investigations into the occurrence, d i s k bution, fate and effects of butyttin compounds in water, sediments and molluscan tissues. These studies were conducted primarily in nearshore harbor locations adjacent to major U.S. Navy ports and harbors to evaluate potential effects of fleetwide implementation of copolymer TBT antifouling coatings (I).