An Eco-Environmental Risk Assessment of Heavy Metal Contamination in Surface Sediments of Lake Yangzong, Southwestern China

Abstract

Heavy metal mitigation is an ongoing environmental problem in aquatic ecosystems. However, a lack of quantitative analysis and accurate evaluation have led to unguided control and water management strategies. Lake Yangzong is the main freshwater resource for nearly one million people in Yunnan Province in southwestern China. It has been heavily polluted in recent years by significant anthropogenic activities including an industrial phosphogypsum spill, sewage effluent, and anthropogenic chemical interference. Herein, we combine eco-environmental indices with multiple statistical analyses to determine the ecological risk and degree of pollution of 11 heavy metals in lacustrine surface sediments. Local background of these metals was determined by robust regression model from sediment cores. Severely As contamination (exceeding 300 mg/kg) was centralized in the southwestern part of the lake and can be attributed to its long-term influx to the lake, rather than a one-time pollution event. Other heavy metal pollutants (e.g., Cd, Cu, Pb) with low to moderate degree decrease progressively from the northwest to the southeast areas of the lake and can be attributed to industrial activities north of the lake. Pollution indices indicate that the northern section of the lake and the southwestern bay exhibit higher contaminant levels than other regions of the lake. Statistical analysis demonstrate that two different types of pollution dominated industrial discharge: mine smelting/coal consumption and re-deposition/sulfuric acid plant tailings leakage. The application of a Hazard Quotient index (HQ) suggests that As also poses a potential risk to children. A develop index Pollution contribute rate (PCR), proposed herein, indicates pollutions were dominated by As and Pb. Bio-toxic indices indicate high ecological risk were mainly attributed to As and Cd.

Keywords: heavy metals, Lake Yangzong, surface sediment, sediment core, eco-environmental indices