Study On Ecological And Geochemical Characteristics Of Cd And Its Pollution Assessment In Black Soil Region Of Jilin Province

For years, cadmium (Cd) pollution occurs frequently both in soil and in food,seriously affecting the stable development of agriculture and ecosystems and posingpotential risks to human health. As an important national commodity grain base,central black region of Jilin could offer billions of kilograms of grain to China eachyear. Therefore, grasping ecological and geochemical characteristics of Cd, itsmigration accumulation and the influencing factors is of great practical significance toprotect ecological environment and human health, and to ensure food quality andsafety in black soil region.Based on collection and test of the samples in central black region of Jilinprovince, this paper summarizes characteristics of Cd content in surface black soil,soil profile and corn seed by taking “soil-plant” as a system. Besides, this paper alsodiscusses Cd activation effect, Cd accumulation in maize seed and their influencingfactors. In addition, Cd pollution in study area is assessed by applying variousevaluation methods and then the conclusions are as follows:1. Characteristics of Cd in surface soilCd content in surface soil of Jilin province is between0.085μg/g and0.284μg/gand its average value is0.145μg/g, which is significantly higher than the backgroundvalues in both Jilin province and China. There is no great difference among averagevalues of Cd total amount in the three working sites, with the following descendingorder: GL (0.159μg/g)＞YS (0.144μg/g)＞JD (0.128μg/g). This indicates that theaverage value of Cd total amount increases from the middle to both the north andsouth of the study area. After analyzing the coefficient of variation of each element, itcould be concluded that the coefficient of variation in GL belongs to moderatevariation whereas ones in both YS and JD belong to low variation.2. Characteristics of Cd in soil profileCd content in YS working region firstly declines and then increases with theincrease of the depth of soil profile, and it is in a natural state. Cd contents in JD and GL behave relatively unstable and they present a “decrease-increase-decrease” trendwith the increase of the depth of soil profile, showing a weak enrichment state.3. Characteristics and influencing factors of Cd available content in surface soilAvailable content of Cd in surface soil is0.015~0.195μg/g, with the averagecontent of0.052μg/g. Among the three working regions, GL has the largest averagecontent of available Cd, with an evident spatial variability, while JD has the smallestone. Cd available content in soil has positive correlations with total content of Cd, andavailable contents of As, Cr, Cu, Mn, Ni and Zn, whereas it exhibits negativecorrelations with available content of Cd and pH value in soil.4. Characteristics and influencing factors of Cd in maize seedCd content in maize seed is ranging from2.00ng/g to6.62ng/g, with an averagecontent of3.15ng/g. The average content of Cd in maize seed has the descendingorder “GL＞JD＞YS” among the three working regions. Cd content in maize seed inblack region, however, does not show significant difference. Cd content in maize seedin study area is far below the upper bound guideline of the national grain Cd standard(0.10μg/g), indicating that corn in black soil region will not affect the health ofhumans and animals.5. Transformation characteristics between “total content-available content” of Cdand influencing factorsThe largest effective coefficient of Cd in black region is0.79while the smallestone is0.11, with the average value of0.34, indicating that it is in the stronglytransformed level. Among the three working regions, the average effectivecoefficients have the following descending order “GL＞YS＞JD”. Moreover,conversion degree of Cd element shows positive correlations with the ones of As, Cr,Cu, Mn, Ni, P, and Zn, while it has evidently negative correlations with pH.6. Cumulative feature of “available content-seed” of Cd and influencing factorsBlack region has the largest cumulative coefficient of0.274and the smallest oneof0.016, with the average value of0.086, showing a very weak cumulative level. Theaverage cumulative coefficients of Cd in the three working regions has the descending order “JD＞GL＞YS”. Cumulative level of Cd exhibited evidently positivecorrelations with the ones of other elements while it has no remarkable correlationwith pH.7. Pollution assessment of Cd in black soil regionWe could arrive at the same conclusion that currently there is no Cd heavy metalpollution in black soil region of Jilin province by the following four methods: singlefactor index, Nemerow index, potential ecological risk index and geo-accumulationindex.