雷州半岛土壤—水稻系统重金属含量特征及其迁移规律

【目的】研究雷州半岛土壤—水稻系统重金属污染程度及稻米的食用风险，以期为雷州半岛开展水稻健康安全食品认证工作提供科学依据。【方法】采集雷州半岛水稻种植地35份表层土壤样品和30份水稻作物样品，采用潜在生态风险指数法和人体健康风险评价方法对土壤—水稻系统中的砷（As）、镉（Cd）、铬（Cr）、铜（Cu）、汞（Hg）、镍（Ni）、铅（Pb）和锌（Zn）元素进行分析。【结果】雷州半岛水稻土壤重金属中Cr和Hg元素的变异系数大于1.000，属于强度变异性，受人为因素影响大；其他6种重金属元素的变异系数介于0.100~1.000，为中等变异强度，受人为因素干扰影响较小；各重金属变异强度大小为Cr>Hg>Ni>Cd>Cu>Pb>As>Zn。通过潜在生态富集系数计算得知土壤重金属Hg的平均潜在生态富集系数为4.657，属于强污染风险；其余7种重金属的潜在生态富集系数在1~3，属于中等污染风险。由潜在生态风险参数得出，廉江市Hg元素为极强污染，在赤坎区和吴川市为很强污染程度，在坡头区为中等污染程度，其余区域则为强污染程度；赤坎区Cd元素为很强污染，廉江市和遂溪县为强污染程度，其余区域为中等污染程度。雷州半岛水稻土壤重金属潜在生态风险指数平均值为309.24，属于强污染风险；各县（市、区）土壤重金属潜在生态风险指数排序为:廉江市>赤坎区>吴川市>遂溪县>雷州市>麻章区>霞山区>坡头区。从健康风险评价结果来看，研究区部分水稻中As、Pb和Cd的含量超过食品安全国家标准（GB 2762—2017），超标率分别为73.33%、53.33%和6.67%，其中As的高危商（HQ）为2.9839，对人体健康存在潜在危害；Cd和Pb的HQ小于1，对人体健康产生的影响不明显。水稻中各重金属元素迁移系数平均值排序为Cd>Zn>Cu>Hg>As>Pb>Cr，其中Cd、Zn和Cu的迁移系数中位值分别为0.9547、0.4900和0.1685，其吸收富集能力强；而Hg、As、Pb和Cr的中位值均小于0.05，其吸收富集能力弱。土壤pH与水稻重金属含量的相关分析结果显示，土壤pH与As呈显著正相关（P<0.05），与Cu和Ni呈极显著负相关（P<0.01）；表明土壤酸性越低，越有利于As元素积累在土壤中，而不利于其他7种重金属元素在土壤中的积累。【结论】雷州半岛水稻田土壤重金属受人类影响越大、理化性质越复杂，其在土壤—水稻系统中的迁移和富集能力越强，以致该地区受污染的程度通常越严重，其中As、Cd和Pb元素含量超标对人体健康存在一定危害，应加强对农业施肥和药剂喷洒以及生活污染的控制，以减轻雷州半岛水稻田土壤的重金属污染程度，保护当地居民健康。

Soil-rice system characteristics and migration regularity of heavy metal content in Leizhou Peninsula

【Objective】In order to carry out the certification of rice for the health and safety of food of rice planting in Leizhou Peninsula，the degree of heavy metal pollution in the soil-rice system and the risk of rice consumption in the Leizhou Peninsula were studied.【Method】Thirty-five surface soil samples and thirty rice crop samples were collected from rice-growing areas in the Leizhou Peninsula. The contents of arsenic（As），cadmium（Cd），chromium（Cr），copper （Cu），mercury（Hg），nickel（Ni），lead（Pb）and zinc（Zn）in the soil-rice system were analyzed by the potential ecological risk index and human health risk assessment methods.【Result】The variation coefficients of Cr and Hg in rice soil heavy metals in the Leizhou Peninsula were greater than 1.000，categorized as high intensity variability and was greatly affected by human factors. The variation coefficient of the other six heavy metals ranged from 0.100 to 1.000，with moderate variation intensity and were less affected by human factors. The variation intensity of heavy metals was Cr>Hg>Ni>Cd> Cu>Pb>As>Zn. According to the calculation of potential ecological enrichment coefficient，the average potential ecological enrichment coefficient of Hg in soil was 4.657，which indicated a strong pollution risk. The potential ecological enrichment coefficients of the other seven heavy metals were between 1 and 3，categorized as medium pollution risk. According to the potential ecological risk parameters，Lianjiang City was highly polluted by Hg，and Chikan District and Wuchuan City were seriously polluted，Potou District was moderately polluted，the rest were strongly polluted. The Chikan District was highly polluted with Cd，with strong pollution in Lianjiang City and Suixi County and moderate pollution in the downtown area. The average potential ecological risk index of heavy metals in paddy soils in the Leizhou Peninsula was 309.24，which was categorized as a strong pollution risk. The potential ecological risk index of heavy metals in soil of each county（city，district）ranked as:Lianjiang City>Chikan District>Wuchuan City>Suixi County>Leizhou City>Mazhang District> Xiashan District>Potou District. From the results of health risk assessment，the contents of As，Pb and Cd in rice in the study area exceeded the national food safety standards（GB 2762-2017）by 73.33%，53.33% and 6.67%，respectively. The high risk quotient（HQ）of As was 2.9839，which posed potential hazards to human health，whereas the HQ of Cd and Pb was less than 1，which had no obvious effect on human health. The average migration coefficients of heavy metals to rice were Cd>Zn>Cu>Hg>As>Pb>Cr and the median migration coefficients of Cd，Zn and Cu were 0.9547，0.4900 and 0.1685，respectively，with strong absorption and enrichment ability. The median values of Hg，As， Pb and Cr were less than 0.05，and their absorption and enrichment ability was weak. The correlation analysis between soil pH and heavy metal content in rice showed that soil pH was significantly positively correlated with As（P<0.05），and was extremely negatively correlated with Cu and Ni（P<0.01），the soil acidity was more favorable for the accumulation of As in soil，but less so for the other seven heavy metal elements.【Conclusion】Heavy metals in paddy soils of the Leizhou Peninsula are more affected by human beings and their physical and chemical properties are complex. The migration and enrichment ability of heavy metals in the soil-rice system is strong，so that the degree of pollution in this area is concerning. The excessive contents of As，Cd and Pb are harmful to human health. Attention should now be paid to agricultural fertilization，pesticide spraying and domestic pollution control，in order to reduce the degree of heavy metal pollution in paddy fields of the Leizhou Peninsula and protect the health of local residents.