The influence of temperature and NaCl on cadmium, copper and zinc partitioning among suspended particulate and dissolved phases in an urban river

Distribution coefficients (Kd) were used to estimate the most important geochemical phases within the suspended particulate matter (SPM) pool for sorption of Cd, Cu and Zn. Given that pH effects were expected to be minimal, as the don is a well buffered system, the possible influence of secondary environmental variables [temperature, dissolved organic carbon (DOC), dissolved Ca2+ and NaC] on trace metal partitioning between SPM and the dissolved phase was evaluated using a series of multiple linear regressions for total (KdT) as well as the phase specific KdL leachable phase; KdR reducible phase; and KdO oxidizable phase) distribution coefficient estimates. The three metals varied in their sorptions patterns. Cd and Zn showed the same relative affinities for three SPM pools (leachable = reducible > oxidizable), while Cu affinities ranked oxidizable = leachable > reducible. Secondary environmental factors were identified as more important influences on trace metal partitioning than pH. Temperature and NaCl (from road salt runoff) were found to be key environmental variables influencing trace metal partitioning. A decrease in water temperature caused decreases in the accumulation of Cd, Cu and Zn in the particulate pool. Increasing NaCl concentrations decreased the concentrations of Cd and Zn associated with the particulate leachable phase and the Cd, Zn and Cu content in the oxidizable SPM phase. These results suggest that in running waters during winter months, or even during summer months in the hypolimnia of sufficiently deep lakes, a relatively higher proportion of these metals remains in the dissolved and potentially more bioavailable pool.