| As is well known, soil is the material foundation of human living and development. Soil quality affects not only crop yields but is also a significant factor governing food safety and agricultural sustainability. Under the double pressures from lack and contamination of water resource, the pollution problem of soil ecological environment deprived from long-term sewage irrigation has been showing seriously and restricting development of sustainable agriculture in China. Therefore, this study was carried out taking sewage-irrigated soil sampled from different area (HS, SJZ, CZ, BD) in low-plain region of Hebei province as research subject. The physicochemical properties, enzyme activities, heavy metal and its fraction in soil and content of heavy metal in crop were determined and analyzed. We assessed the fertility quality, environment quality, comprehensive quality of soil and health risk of crop. The main problems of sewage-irrigated soil in different sampling area of Hebei province were revealed. The results will play an important role in suppressing soil environment quality decrease, improving soil fertility, and ensuring food safety for the sewage-irrigated area of Hebei province. The major findings were summarized as follows:(1) The sewage-irrigated soil in Hebei province was loam, including medium loam for HS, SJZ, BD and heavy loam for CZ. As far as pH of 0～20cm soil samples were concerned, the proportion of 6.5～7.5 reached more than 50% in SJZ and BD, whereas more than 80% of soil samples were alkaline(7.5～8.5) in CZ and HS. Additionally, more than 90% of 20～40cm soil samples were still alkaline in the all sewage-irrigated area.According to soil fertility standard of the second national soil survey and current situation of soil fertility in Hebei province, the organic matter, total potassium and available potassium contents of 0～20cm sewage-irrigated soil were in the medium-high level. The total nitrogen and phosphorus, available nitrogen and phosphorus content were in low level. Among the four sewage-irrigated area, the organic matter, nitrogen, phosphorus and potassium content in SJZ were the highest. The urease, catalase, alkaline phosphatase and invertase activities were correlated with mostly physicochemical properties in a significant or very significant way. On the whole, enzyme activities of sewage-irrigated soil in BD and SJZ were higher, but the lower soil enzyme activities were recorded in HS and CZ, especially for urease activity. The physicochemical properties and enzyme activities of sewage-irrigated soil were lower in 20～40cm soil layer than in 0～20cm soil layer and decreased in significant difference of four sewage-irrigated areas.The present situation of fertility quality of 0～20cm sewage-irrigated soil was evaluated by using fuzzy mathematical method. The results showed that soil fertility quality index(SFQI) for HS, SJZ, CZ and BD was 0.42,0.67,0.40 and 0.61, respectively in moderate, higher, moderate and higher fertility level.(2) The contents of heavy metals in sewage-irrigated soil sampled from low-plain region of Hebei province followed the order of Fe>Ti>Mn>Zn>V>Cr>Pb> Cu> Ni>Co> As>Sn>Cd>Hg(Cu>Pb in 20～40cm). Except for Fe, Mn and As, the average concentrations of other heavy metals in SJZ were the highest. Compared with the background values of heavy metals in Hebei province, an accumulation level of heavy metals was significant in the sewage-irrigated soils, especially for Hg, Cd, Zn and Pb, which were beyond the permissible limits set by the State Environmental Protection Administration(SEPA) and Ministry of Agriculture(MA) in China. The proportion of soil samples was exceeded by 44.4% for Cd and 8.9% for Pb, respectively. The principal component analysis(PCA) in combination with cluster analysis (CA) revealed that heavy metal contamination had different origination. The primary inputs of Cd, Cr, Cu, Pb, Sn and Zn in sewage-irrigated soils were due to anthropogenic sources, whereas As, Fe, Mn, Co, Ti and V were mainly of pedogenic source. A considerable proportion of the mostly heavy metals resided in residual fractions, whereas Cd and Cr dominated the exchangeable fraction.An assessment of soil environmental quality and its warning results revealed that the study area was higher enrichment level with respect to Hg, Cd, Zn, Pb and Cu, which led the contamination of soil and posed severely ecological risk. The degree of comprehensive ecological risk in SJZ was very strong; and moderately to strongly warned with 57.15% relative level. The degree of comprehensive ecological risk in CZ and BD was stronger; and moderately to strongly warned with 25.00% and 6.67% relative level, respectively. The degree of comprehensive ecological risk in HS was moderate; and no warned with 94.44% relative level.(3) Concentrations of Pb and Hg in grain seeds(except for cotton seed) selected from the sewage-irrigated soil were beyond the safe limit of pollutants in food of China (GB2762–2005); and the contamination with Pb and Hg was at its higher level in wheat seed(8.5% and 16.7%) than in maize seed(6.0% and 10.0%). Concentrations of Zn, Ni, Pb, Cd and Hg in leafy vegetables (except for cauliflower) selected from the sewage-irrigated soil were beyond the safe limit of pollutants in food of China (GB2762–2005); more than 50% leafy vegetable samples contaminated with Pb and Cd were found in edible parts of spinach; and between 10% to 30% leafy vegetable samples contaminated with Zn, Ni, Pb, Cd and Hg appeared to all edible parts of Chinese cabbage, rape, parsley, and chives. Concentrations of Zn, Ni, Pb and Cd in root vegetables (except for scallion) selected from the sewage-irrigated soil were beyond the safe limit of pollutants in food of China (GB2762–2005); and all the root vegetable samples contaminated with Pb were found in edible parts of mustard and white radish, which were related to higher enrichment factor of heavy metals in root vegetables grown in sewage-irrigated soil.The health risk index(HRI) of single heavy metal for crops grown in sewage-irrigated soil suggested that the consumption of mustard and maize posed a higher health risk for Pb and Ni, respectively; but other vegetables were free of health risks. However, the combined total health quotients (THQ) exceeded the safe level(THQ>1) and were not free of risk for maize, mustard, spinach, white radish, parsley and rape. In all crops THQ for children were higher than that for adults.The species of crops, available fraction of heavy metal and food health standard were all taken into consideration for establishing available heavy metal fraction thresholds based on soil-plant system in the sewage-irrigated area. The threshold values of exchangeable fraction of Pb,Zn,Cd and Cr were 4.47 mg kg-1, 10.99 mg kg-1, 0.27 mg kg-1 and 42.38 mg kg-1 for grain growing soil, 8.45 mg kg-1, 16.38 mg kg-1, 0.15 mg kg-1 and 52.97 mg kg-1 for vegetable growing soil, respectively. The threshold values of carbonate fraction of Pb and Cr were 1.75 mg kg-1 and 8.83 mg kg-1 for grain growing soil; and 42.37 mg kg-1 of Zn for vegetable growing soil. The threshold values of iron/manganese oxide fraction of Zn and Cr were 67.08 mg kg-1 and 14.29 mg kg-1 for grain growing soil; and 31.19 mg kg-1 of Cr for vegetable growing soil.(4) Principal component analysis (PCA) output using Box-Cox normalization on raw dataset of physicochemical properties, enzyme activities, available heavy metals in 0～20cm sewage-irrigated soil demonstrated that comprehensive soil quality in HS was the best; the worst comprehensive soil quality was found in SJZ; and the moderately comprehensive soil quality was recorded in BD and CZ. The difference in four sewage-irrigated areas was also significant (P<0.05).Therefore, the effective remediation technologies, strict protection measures, stringent guidelines and an integrated system for sewage-irrigated soil are needed to enhance its environmental quality and avoid polluted accidents in the SJZ area, because the lowest environmental quality and comprehensive quality and highest fertility quality of soil were found in SJZ. Additionally, the physicochemical properties, enzyme activities, heavy metals concentrations and so on, which reflect status of soil quality, should be long-term and periodically monitored in the sewage-irrigated soils together with the improvement measures of soil fertility and practice of perfect cropping pattern to minimize possible impacts on human health and get the agricultural sustainability in sewage-irrigated soil.
|
PDF Full Text Request