Distribution and variation of metals in urban river sediments in response to microplastics presence, catchment characteristics and sediment properties.

Despite well documented studies on metal pollutants in aquatic ecosystems, knowledge on the combined effects of catchment characteristics, sediment properties, and emerging pollutants, such as microplastics (MPs) on the presence of metals in urban river sediments is still limited. In this study, the synergistic influence of MPs type and hazard indices, catchment characteristics and sediment properties on the variability of metals present in sediments was investigated based on a typical urban river, Brisbane River, Australia. It was noted that the mean concentrations of metals in Brisbane River decreases in the order of Al (94,142 ± 12,194 µg/g) > Fe (62,970 ± 8104 µg/g) > Mn (746 ± 258 µg/g) > Zn (196 ± 29 µg/g) > Cu (50 ± 19 µg/g) > Pb (47 ± 25 µg/g) > Ni (25 ± 3 µg/g) while the variability of metals decreases in the order of Pb > Cu > Mn > Al > Ni > Zn > Fe along the river. According to enrichment factor (Ef) contamination categories, Mn, Cu and Zn exert a moderate level of contamination (Ef > 2), while Fe, Ni, and Zn show slight sediment pollution (1 3) was found at sampling locations having a high urbanisation level and traffic related activities. Crustal metal elements (namely, Al, Fe, Mn) were found to be statistically significantly correlated with sediment properties (P < 0.05). Anthropogenic source metals (namely, Cu, Ni, Pb, Zn) were observed to be highly correlated with catchment characteristics. Additionally, the presence of metals in sediments were positively correlated with MPs concentration, and negatively correlated with MPs hazard indices. The outcomes of this study provide new insights for understanding the relationships among metals and various influential factors in the context of urban river sediment pollution, which will benefit the formulation of risk assessment and regulatory measures for protecting urban waterways.

Influence of microplastics on nutrients and metal concentrations in river sediments.

Microplastics pose threats to aquatic environments because they serve as hard-substrate for microbial community colonization and biofilm formation due to their long-life span and hydrophobic surface which can impact on aquatic ecosystems. However, the association between microplastics and other pollutants, particularly nutrients and metals in river sediments are largely unknown. In this study, microplastics abundance and hazard scores which are the risks arising from chemical compounds used for plastics manufacture, and the correlations between microplastics and the concentrations of total carbon (TC), total nitrogen (TN), total phosphorus (TP) and metals commonly present in the urban environment such as Al, As, Cr, Co, Cu, Fe, Mg, Mn, Ni, Cd, Se, Sr, Zn, Pb, in Brisbane River sediments were investigated. The study confirmed that the risk associated with microplastics is based on their monomer composition rather than the quantities present. Sediments having relatively higher abundance of microplastics with a relatively lower hazard score result in higher nutrient concentrations. The concentrations of metals in river sediments are more dependent on their original sources rather than the concentration of microplastics. Nevertheless, leachate from plastics should be considered in risk assessment in relation to the association between metals and plastics in aquatic environments.