Distribution of Copper in Sediments from Fluvial Reservoirs Treated with Copper Triethanolamine Complex Algicide

Abstract

The control of algal growth in water reservoirs with copper-based algicides leads to elevated sediment Cu concentration and thus could affect long-term water quality. To assess the potential mobility of sediment-associated Cu, a study was conducted using samples from three drinking water reservoirs treated with Cutrine®, a copper triethanolamine complex algicide. Total Cu (CuT) in treated reservoir sediment ranged from 13.3 to 139.9 mg Cu kg−1 and was on average 1.5 times the level in streams (48 mg Cu kg−1) flowing into the reservoirs. Sediment CuT and algicide application history indicated the retention of 82–93% of the algicide Cu applied. Sequential extraction showed that Cu primarily accumulated in the residual fraction (60%), whereas the potentially mobile pools (water extractable: CuH2O, exchangeable: CuEX, organic bound) accounted for <10% of CuT. The leachable Cu fraction (extracted with 1 M acetic acid) also amounted to <9% of CuT and was related negatively to C/N and positively to H/C ratios of organic matter. In addition, these potentially mobile fractions were found to be related, not to total organic C, but to sediment respiration suggesting that the potentially mobile Cu fractions were primarily associated with aliphatic and readily biodegradable C (more so than total organic C). During a 2-year period without algicide treatment (that followed 4 years of repeated algicide applications to one of the studied reservoirs), mean dissolved Cu (micrograms per liter) in the reservoir (39.2) was similar to levels measured at locations upstream (43.3) and downstream (47.2) from the reservoir. These results indicate that the bulk of sediment Cu is associated with geochemically stable solid phases and thus should alleviate concerns about Cu transfer into the water column.