Historical sources and ecological risk trends of typical toxic pollutants in sediments from Taihu Lake, Yangtze Delta, China

The long-term changes of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) in sediments can reflect the ecological risks (ER) caused by their pollution sources in different historical periods. This is of great significance to the improvement of environmental protection policies in the future. The study area is located in Taihu Lake, China. 137Cs and 210Pb were used for dating. Indicators related to local socio-economic development were introduced to optimize source identification in the absolute principal component score multiple linear regression (APCS-MLR) model. On this basis, the mean effect range median quotient (M-ERM-Q) method was used to evaluate the ER of source-oriented HMs and PAHs at different ages. The HMs content was relatively stable from 1949 to 2015, and then increased significantly. The PAH contents were on the rise during the whole historical period. The average contribution rate of traffic emission and fertilization to HMs was 50.59 % and 49.41 %. Ecological risk caused by Traffic emitted pollutants was relatively stable before 2015, then increased sharply, and finally reached a medium-high level. However, fertilization ER has always maintained an increasing trend and accelerated after 1980, ultimately reaching medium-low ER. The contribution rates of coal combustion, mixed sources (biomass and coal) and gasoline combustion to PAHs were 13.20 %, 52.45 % and 34.36 %, respectively. The ER of mixed sources and gasoline combustion showed a gradually increasing trend before 2007, and then began to decrease. However, coal combustion ER has been increasing, and the increase accelerated in 2000. Nevertheless, the ER of these three sources was still low. Overall, a certain degree of HMs pollution has been caused by traffic emissions and fertilization in recent years. Local governments should prioritize the control of these two sources to protect the Taihu Lake ecosystem.