The effect of UV-induced changes in dissolved organic matter (DOM) on the uptake of copper and cadmium in caddisfly (Hydropsyche sp.) larvae

The effect of photolysis on the binding of dissolved organic matter (DOM) to metals in aquatic systems was examined. In three replicated experiments, water from a wetland with 20–30 mg C/L of dissolved organic carbon (DOC) was subjected to UV-A and UV-B over periods of time varying between 0 and 12 days in a laboratory setting. Changes in both concentration and structure of the DOC were observed. Stable isotopes of Cd and Cu were added to the UV-irradiated water, to which caddisfly larvae (Hydropsyche sp.) were exposed for 3 days. The larvae were subsequently analyzed by ICP-MS for metal uptake. Structural changes in DOM resulted in a significant increase in Cu uptake within 4 days of UV exposure. When bioconcentration factors were normalized for DOC this change was significant at all stages of DOM breakdown, indicating that structure exerted an important influence on the bioavailability of Cu. Changes in Cd uptake were not attributed to DOM breakdown, and other influences (pH and water hardness) are probably the cause of observed changes. Similar research in soft water and low pH systems is recommended.