Distribution and Sources of Dissolved and Particulate Heavy Metals (Mn, Co, Ni, Cu, Zn, Cd, Pb) in Masan Bay, Korea

In this study, we investigated the spatial and temporal distribution and sources of dissolved and particulate heavy metals in Masan Bay, an area that for a long time has been contaminated by waste from surrounding large industrial complexes and metropolitan cities. Surface seawater samples from 16 sites around inner Masan Bay and offshore were collected over four survey periods (October 2015 and June, August, andNovember 2016). The spatial gradients of dissolved and particulate heavy metal concentrations generally overwhelmed the temporal variability, with a sharp decrease in metal concentrations, as well as salinity, with distance from the innermost site near the river mouth toward offshore. This tendency was maintained throughout all four survey periods. With the exception of zone I (sites 1-4), the concentrations of dissolved and particulate heavy metals showed little spatial variability, although possible sources of heavy metals, such as wastewater treatment plants (WWTPs; Dukdong and Jinhae), were located in the area. The main sources of several heavy metals would be the river water itself, as well as the release processes of river particles. Metal-enriched biological particles from river water and WWTP effluent were the main contributors to the particulate metal concentrations during June and August; however, during October and November, the particulate metal concentrations were supplied by detrital particles similar to sediment. The contamination index was calculated using metal concentrations in offshore samples as the background concentrations. Mn, Co, and Zn contamination in zone I ranged from grade 3 to 5, indicating moderate to strong pollution conditions.