Sediment evidence of industrial leakage-induced asynchronous changes in polycyclic aromatic hydrocarbons and trace metals from a sub-trophic lake, southwest China

Sediment core records and impact factors of polycyclic aromatic hydrocarbons in Chinese lakes

Lake sediment is a natural sink for polycyclic aromatic hydrocarbons (PAHs). PAH sedimentation characteristics and their impact factors of Chinese lakes have mainly been qualitative assessed. However, quantitative impacts of PAH sedimentation from different factors have not been well analyzed. To fill this gap, we screened PAH sedimentation records from the literature, for 51 lakes in China and other regions of the world, to identify historical concentration variation and the impact factors of PAHs in different regions, in lake sediment. The results show that PAH concentrations in the sediment core in the selected Chinese lakes (478 ± 812 ng/g dry weight (dw)) were significantly lower than those in North America (5518 ± 6572 ng/g dw) and Europe (3817 ± 4033 ng/g dw). From 1900 to 2015, most of the lakes in China showed an increasing trend of PAH sedimentation concentrations, with the lakes in Southeastern China showed a decreasing trend of PAH concentration in the period of 2001-2015, which was later than the peak times shown in Western countries (1941-1970). The 2-3-ring PAHs were the main components in the sediment core of Chinese lakes, but the proportion to the total PAHs decreased from 72% in 1900-1940 to 55% in 2001-2015. Generalized additive modeling (GAM) was adopted to simulate the associations between PAH sedimentation records and the impact factors. There are large regional variations of economic and industrial development in China. The impact factors of PAH accumulation in the lake sediments differ in different regions. However, population and the consumption of coal, pesticides, and fertilizer were identified to be the most important impact factors influencing PAH sedimentation. The Chinese government needs to strengthen control measures on pollutant discharge to reduce the anthropogenic impact of PAH sedimentation in lakes.

Contamination and eco-risk assessment of toxic trace elements in lakebed surface sediments of Lake Yangzong, southwestern China

Toxic trace elements represent an ongoing environmental problem in aquatic ecosystems. However, a lack of quantitative analysis and accurate evaluation has 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 contaminated in recent years by significant anthropogenic activities including an industrial phosphor-gypsum spill, sewage effluent, and chemical remediation processes. Herein, we combine eco-environmental indices with multiple statistical analyses to determine the ecological risk and degree of contamination of 11 toxic trace elements in the upper sediments of the lakebed. Local geochemical background concentrations were determined using robust regression models developed from sediment core data. Pollution indices (EF/PLI) indicate that severe As contamination was centralized in the southwestern part of the lake. Other toxic trace elements (e.g., Cd, Cu, Pb) are slightly to moderately enriched, and progressively decrease from the northwestern to the southeastern areas of the lake. A more accurate and sensitive index (PCR) was proposed herein, suggesting that contamination was dominated by As and Pb in different lake sections. The northern section of the lake and the southwestern bay exhibited higher contaminant levels than other regions of the lake. Bio-toxic indices (ERF/PERI) indicate that As and Cd pose a high ecological risk, whereas Cu and Pb pose a low risk to biota. Statistical analyses (PCA/PMF) demonstrate that metal contaminants originated from three types of anthropogenic sources: the smelting of metal ores, the leakage of tailings effluent, and coal consumption.

Spatio-temporal variations of sedimentary metals in a large suburban lake in southwest China and the implications for anthropogenic processes

Environment quality of suburban and urban lakes receives special attention due to their great impacted by human perturbations and important roles in ecosystem services. Herein, the spatio-temporal variations of 10 metal and metalloid elements in 13 sediment cores from a large suburban lake (Dianchi) were studied to explore the changes in sedimentary environment and pollution and their associations with human activities since the last century. Concentrations of each element were largely varied at spatial scales, but showed similar vertical trends among the profiles, suggesting comparable changes in sedimentary processes in each lake region. Cluster analysis showed two groups of elements: group I includes Al, Ti, Cu, Cr and Ni, and group II includes As, Cd, Hg, Pb and Zn. Temporally, concentrations of all elements were generally constant until the 1950s. Thereafter, group I elements along with the clay percentage started to decrease, indicating accelerated input of coarser soils due to strengthening human perturbation and changing land use. However, group II elements showed increasing values of concentrations, particularly the enrichment factors (EF = 1.0-10.8), which peaked between mid-1990s and 2000, indicating continued pollutants input with watershed economic development. With the implementation of environment management measures, pollution was initially restrained or reduced in recent decades as indicated by the stable EFs and sedimentary fluxes of Cd, Hg, Pb and Zn and decreasing values of As. Spatially, the stocks of anthropogenic As, Cd, Hg, Pb and Zn were higher in the northern while lower in the southern lake area. This spatial difference was mainly due to the large input of industrial and domestic wastewaters in the northern compared to the area in the southern that receives runoff from agricultural and forested land. Overall, the spatio-temporal patterns in accumulation of metal and metalloid elements in the lake reliably reflected the impacts of watershed human activities.

Environmental legacy and catchment erosion modulate sediment records of trace metals in alpine lakes of southwest China

Sediment records are widely used to infer impact of atmospheric metal deposition in alpine lakes, however, the legacy effect and catchment erosion of historical pollutants could potentially affect metal influx into lakes. Here, we collect data (including six trace metals and three lithogenic elements) from well-dated sediment cores of seven alpine lakes in southeast Tibet, which is adjacent to southwest China. This area has a documented history of preindustrial pollution. Metals such as cadmium (Cd), zinc (Zn) and arsenic (As) are found at relatively low concentrations until a clear increase is observed after 1950s across lakes. This result is consistent with accelerating atmospheric metal deposition due to socio-economic development in the region. We observe no synchronous trend across lakes in the changes of lead (Pb), copper (Cu) and silver (Ag), which show no significant increase after ∼1950 over the last two centuries in most of the study lakes. The historical trends of ²⁰⁶Pb/²⁰⁷Pb ratio reflect an important source of anthropogenic Pb associated with preindustrial mining and smelting in this study region, suggesting a substantial impact of legacy contamination from ancient mines. Furthermore, the temporal variations in these six anthropogenic metals are largely accounted for by terrigenous elements (e.g. aluminum (Al) and titanium (Ti)) in most of the study lakes, and to a lesser degree by sediment grain sizes and organic matter content, suggesting a significant role of catchment erosion in modulating sediment metal signals. In all, this study highlights the legacy effect of historical pollutants may have enhanced the forcing of catchment erosion in modulating the sediment signals of anthropogenic deposition in southeast Tibet.

Anthropogenic PAHs in lake sediments: a literature review (2002-2018)

Lake sediments are an important reservoir for toxic and hydrophobic polycyclic aromatic hydrocarbons (PAHs). Monitoring of PAHs in sediment is helpful to understand pollution mechanisms and anthropogenic activities. This study reviews studies of PAHs in lake sediments published during 2002-2018. The studies' findings are analyzed, distributions of PAHs in lake sediments are summarized, and the applicability of lake sediments for tracking changes in PAH emission sources is emphasized. Lake sediments heavily polluted with PAHs are distributed in China, Egypt, the USA, and some urban lakes in Africa. The high levels of PAHs are predominantly associated with human activities such as anthropogenic combustion, petroleum industries, road traffic, and socioeconomic factors. However, the concentrations of sedimentary PAHs in most lakes were below the international guideline values.