Quantification of copper doses to settlement plates in the field using diffusive gradients in thin films

Difficulty in estimating toxicant exposure has impeded the development of field-based experiments that examine the effects of toxicants in natural situations. In this study, diffusive gradients in thin films (DGT) were used to measure doses of copper delivered to settlement plates in the field over 30 days. Measurements were made at 4 sites near Melbourne, Australia, inside and outside of two enclosed marinas, and at two times designed to coincide with periods of warmest and coolest water. Dose was initially high, but dropped off sharply over the 30-day exposure period. Dose was affected by site, with more than an order of magnitude difference in the average dose between some sites. Hydrological factors were probably mainly responsible for the differences in dose observed. Dose varied with time of year, but the effect was site specific and was probably mediated by several factors. Measurements were affected by the presence of diffusive boundary layers and fouling, and procedures designed to eliminate the effects of diffusive boundary layers and fouling were highly sensitive to analytical errors and outlying data points. Despite this, the technique was able to show that field doses were comparable to those used in laboratory tests, and that acutely toxic conditions can be generated in natural situations.