Soil Salinization and Heavy Metal Pollution in Asparagus Growing Areas of Chongming Island, China

Chongming Island was located at the mouth of the Yangtze River and had fertile soil, making it one of the vegetable production bases in Shanghai. Asparagus was a kind of vegetable with rich nutrition and crisp taste, which became the characteristic vegetable grown in Chongming Island. With the rapid development of science and technology, industrialization accelerated, and urbanization entered the fast lane. Agriculture encountered many problems in the development of production. A large amount of waste from industrial development was discharged, and the unscientific use of land caused a decrease in soil utilization. The problems of soil salinization and heavy metal pollution in the agricultural environment became severe. The lack of soil salinization and soil heavy metal pollution characteristics and the risk assessment of the quality and safety of asparagus agricultural products were carried out specifically for asparagus growing areas. Therefore, this paper selected Chongming Island farmland soil and its planted asparagus as the research object, conducted sampling research, carried out soil main salinization detection and health risk evaluation methods, studied the degree of salinization of soil heavy metals in the vegetable base, soil heavy metal pollution characteristics, with potential health risks, and provided basic data on soil salinity characteristics and heavy metal pollution content for asparagus base industrial layout.

The results of the study showed that. Cations were determined in the soil of the asparagus planting area: K+, Na+, Ca2+, Mg2+. The average contents were 0.109, 0.174, 0.441, 0.134 g/kg, and the contents of K+ and Mg2+ were low. The coefficient of variation of Mg2+ was the highest among cations at 0.748. Ca2+ content was the highest, accounting for 51% of the total water-soluble cations. The anions HCO- 3, SO2- 4, and Cl- were dominant in the soil of the asparagus growing area, CO2- 3 was less present, and the average contents of HCO- 3, Cl-, and SO2- 4 were 0.013g/kg, 0.176g/kg, and 0.592g/kg, and the content of SO2- 4 was higher in the soil. The coefficient of variation of Cl- among the anions was the largest at 0.761. The types of soil salinization were sulfate-chloride, chloride-sulfate, and sulfate. Mildly saline soils occurred in part B.

The mean contents of As, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Zn, and Hg in the surface soil of Chongming Island were 11.726, 5219.766, 0.192, 52.686, 65.298, 29608.889, 4215.255, 474.241, 23.902, 21.11 116.038, 0.214 mg/kg.(GB15618-2018) None of the risk control value elements specified in (GB15618-2018) were exceeded. Compared to the background values, Mg, Zn, Cu, As, Hg, Cd in the soil showed different levels of accumulation, while Mn, Ni, and Pb showed a decrease. The low coefficients of variation in the soil were As, and the moderate variation was Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Zn, and Hg belong to high variation. From the geological cumulative index, the average value of As was slightly polluted, and the whole was slightly polluted; Cd was not polluted, but there was a local slight pollution state; Cr was not polluted; Cu was not polluted, but there was a local slight pollution state; Mn was not polluted; Ni was not polluted; Pb was not polluted; Zn was not polluted, but there was a local Hg was non-polluted, but there was a local minor pollution.

The amount of Cr in the edible part of asparagus in the study area exceeded the limit value of the national food safety standard (GB 2762-2022), while the content of other elements was below the limit value. Asparagus had the highest enrichment coefficient for Zn and the lowest for Pb. The trend of bioconcentration coefficients was: Zn > As > Ca > Cd > Cr > Cu > Fe > Hg > Mg > Mn > Ni > Pb. The risk of Cr was the highest among the five non-carcinogenic metals for both adults and children, and the risk of Cr was also the highest among the five carcinogenic metals for children, with the highest carcinogenic risk for both adults and children exceeding 1 ￗ 10 -4.

The main conclusion: the soils in the asparagus growing area of Chongming began to appear slightly saline, and the mean concentrations of Cr in asparagus were all higher than the national standard limits. Asparagus base soil heavy metal mercury spatial specific coefficient of variation was the highest, probably anthropogenic activities lead to a large coefficient of variation on the distribution of soil heavy metals significantly higher shadow, children through the dietary route intake of heavy metals are more than adults, higher health risks. The carcinogenic risk values of heavy metals Cd and Cr exceeded the safety line, and there was some health risk.