Environmental Behaviors And Ecological Effects Of Heavy Metals In Agricultural Soil In Dehui, Jilin Province

Soil contamination with heavy metals draws great attention due to its potentialthreat to food safety, human health, and its detrimental effects on soil ecosystems.Excessive accumulation of heavy metals in agricultural soils can be transferred fromsoil to crops, and can affect human health through the food web. Food consumptionhas been identified as the major pathway of human exposure compared to other waysof exposure such as inhalation and dermal contact. The black soil region in NortheastChina is one of the major bases for commercial grain production in China, soilcontamination affects food safety. This research studied the environmental behaviorsand ecological effects of heavy metals in agricultural soil in Dehui, a representativeagricultural area in the black soil region, Northeast China. This research is essential toreduce metal inputs and to establish quality standards on a regional level that allowthe detection of sampling sites affected by pollution.The coefficients of variation varied from12.2%for Zn to45.0%for Cu, itdecreased in the order Cu>Pb>Ni>Cr>Zn, showing the significant influence ofagronomic practices on soil Cu and Pb contents. The coefficients of variation for Cr,Ni, and Zn were small, and the mean concentrations of Cr, Ni, and Zn were lowerthan their background values, indicating that anthropic inputs of these elements werelow. The results of PCA for heavy metal contents showed that soil Cr, Ni, and Zn hada lithogenic origin, whereas, the elevated Cu concentrations in the study area were associated with industrial and agronomic practices, and the main sources of Pb wereindustrial fume, coal burning exhausts, and domestic waste.The trends for soil Cr, Ni, and Zn were similar with higher concentrations trendingN–S across the centre of the study area, other hotspots were located in the southwestof the area. The concentrations of Cr, Ni, and Zn pointed to the parent materialinfluence, and their spatial distribution showed a good correlation with the surfaceevidence of the mineralogical structure. The spatial distribution of Cu and Pb wereaffected by human activities. High Cu values can come from Cu-based agrochemicalsrelated to specific agronomic practices; the hotspots of Cu were coincided with thevegetable farming area. The hotspots where the soils were enriched with Pb mostlycoincided with the towns and big villages that had a high discharge of industrial fume,coal burning exhausts and domestic waste.Cultivation affects soil organic matter and its fractions, and affects metaldistribution in humic and fulvic acid in black soil. Uncultivated sites and theiradjacent cultivated sites (18,50, and>200years) were studied in the present study,the results showed that the content of dissolved organic carbon (DOC), soil organiccarbon (SOC), extractable humic substances (HS), and humin (HU) had decreasedafter200years of cultivation. SOC had decreased by30%after200years ofcultivation. Cultivation led to a moderate decrease (38%) in HA and a minor decrease(7%) in FA. The CHA/CFAratio, which is a humification parameter, decreased from2.05in the uncultivated soil to1.38in the soil cultivated for200years, showing a33%decrease, and indicating a lower degree of humification of organic matter incultivated soils.Lead and Zn were more abundant in the FA than the HA fraction. TheFA-complexed Pb and Zn (%of total Na4P2O7+NaOH-extracted Pb and Zn) were inthe ranges47–60%and63–76%, respectively, showing that fulvic acid has a highaffinity for Pb and Zn. Binding on HA may enhance metal sorption on mineralparticles, and accordingly decrease the mobility of heavy metals. In the present study,relatively higher Zn and Pb concentrations were found in the FA fraction, evidencingthat these elements have high phytoavailability. Copper was bound predominantly to the HA fraction;55%of the Na4P2O7+NaOH extracted Cu was in the humic fraction.The share of Cu and Zn in the HA fraction decreased with cultivation time, butcultivation did not bring about a systematic change in Pb distribution in humicsubstances. The results show that cultivation can decrease the humified C content andmetals bound to the HA fraction, and suggest that cultivation may potentially increasethe mobility of heavy metals.Risk assessment of heavy metals in agricultural soil showed that soil Cr, Ni, Cu, Zn,and Pb in the study area belonged to low potential ecological risk for all the samplingsites. Anthropic activities caused an enrichment of Cu and Pb in soils. However, metalconcentrations in all agricultural soils did not exceed the concentration limit affectingthe safety of agricultural production and human health according to the soilenvironmental quality standard of China, indicating an insignificant contamination ofthese metals in the area.