Abstract
Metals and metalloids accumulate in soil, which not only leads to soil degradation and crop yield reduction but also poses hazards to human health. Commonly, source apportionment methods generate an overall relationship between sources and elements and, thus, lack the ability to capture important geographical variations of pollution sources. The present work uses a dataset collected by intensive sampling (1848 topsoil samples containing the metals Cd, Hg, Cr, Pb, and a metalloid of As) in the Shanghai study area and proposes a synthetic approach to source apportionment in the condition of spatial heterogeneity (non-stationarity) through the integration of absolute principal component scores with geographically weighted regression (APCA-GWR). The results showed that three main sources were detected by the APCA, i.e., natural sources, such as alluvial soil materials; agricultural activities, especially the overuse of phosphate fertilizer; and atmospheric deposition pollution from industry coal combustion and transportation activities. APCA-GWR provided more accurate and site-specific pollution source information than the mainstream APCA-MLR, which was verified by higher R2, lower AIC values, and non-spatial autocorrelation of residuals. According to APCA-GWR, natural sources were responsible for As and Cr accumulation in the northern mainland and Pb accumulation in the southern and northern mainland. Atmospheric deposition was the main source of Hg in the entire study area and Pb in the eastern mainland and Chongming Island. Agricultural activities, especially the overuse of phosphate fertilizer, were the main source of Cd across the study area and of As and Cr in the southern regions of the mainland and the middle of Chongming Island. In summary, this study highlights the use of a synthetic APCA-GWR model to efficiently handle source apportionment issues with spatial heterogeneity, which can provide more accurate and specific pollution source information and better references for pollution prevention and human health protection.
Highlights
Licensee MDPI, Basel, Switzerland.Soil is one of the most important material bases for human survival and development and for guaranteeing food security and human health [1,2]
Long residence time, and great bioaccumulation and biomagnification via the food chain, toxic metals and metalloids (TMMs) accumulation in agricultural soils leads to soil degradation and crop reduction and poses hazards to human health through various exposure pathways [8,9,10,11,12]
Chongming Island is the largest agricultural planting base in Shanghai [47] and the southern area, including the Jinshan and Fengxian districts, which are zones where intense agricultural activities occur [41]. These results indicate that, in some specific areas, agricultural activities, especially the overuse of phosphate fertilizer and pesticides, were the main sources of As and Cr pollution, which were different from the overall APCA-MLR analysis, showing that As and Cr were mainly derived from natural sources across the study area
Summary
Licensee MDPI, Basel, Switzerland.Soil is one of the most important material bases for human survival and development and for guaranteeing food security and human health [1,2]. China, increased levels of pollutants, including toxic metals and metalloids (TMMs), have accumulated in soils, which have caused critical environmental problems and pose serious hazards to human health [3,4,5]. The proportion of samples for TMM concentrations higher than their corresponding background values was in the decreasing order of Cd (46.94%) > Hg (43.81%) > Cr (41.81%) > As (37.97%) > Pb (35.42%) (Table 1), indicating that a certain amount of TMM accumulation has occurred in agricultural soils due to human activities, of which the accumulation of Cd and Hg was more serious. The proportion of samples with TMM concentrations higher than their corresponding risk screening values was in the decreasing order of Cd (3.03%) > Hg (0.38%) > As (0.11%) > Pb (0.05%) > Cr (0.00%) (Table 1), indicating that the soil was relatively safe for agricultural production and human health. Cd and Hg showed high variation, Pb and As showed moderate variation, and Cr showed low variation
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