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.