Contamination status of Pb and Cd and health risk assessment on vegetables in a mining area in southern Hunan

Vegetables,including leafy vegetables and fruit,are of importance to human health. In order to evaluate the heavy metal contamination status and associated health risks of vegetables,57 vegetables( 34 spring vegetables and 23 winter vegetables) and 34 corresponding soil samples( sampled with the spring vegetables) were collected from farmland surrounding a mining area in southern Hunan,China. Analysis was carried out to determine the correlation between the heavy metal content of vegetables and soils,to enable assessment of the potential health risk to local inhabitants consuming the vegetables grown in the contaminated soils. The results showed that:( 1) The measured maximum total Pb and Cd in the soils were up to 1251. 9 mg / kg( the corresponding soil to the three-colored amaranth) and 13. 2 mg / kg( the corresponding soil to the kidney bean),respectively. The average concentration of total Pb and Cd in all soils were 841. 7 mg / kg and 6. 5 mg / kg,respectively,which were 3. 37 and 21. 67 times the standard allowable concentration of Pb and Cd for vegetable soils in China( pH level 6. 5,Pb ≤ 250 mg / kg,Cd ≤ 0. 3 mg / kg; Environment Quality Standard for Soil Heavy Metals GB15168—1995,Grade II). It suggested that contamination from heavy metals in these soils was very serious.( 2) Vegetables grown on the contaminated soils were rich in Pb and Cd in different plant organs. The highest levels of heavy metals were 5. 03 mg / kg for total Pb and 2. 92 mg / kg for total Cd in the edible parts of garlic and threecolored amaranth,respectively,which exceeded the maximum levels of the China National Food Sanitation Standards fortotal Pb( GB 14935—94,0. 2 mg / kg) and Cd( GB 15201—94,0. 05 mg / kg). The heavy metal content of leafy vegetables,not fruit,exceeded the China National Food Sanitation Standards for Heavy Metals. The contents of total Pb and Cd in different organs of the vegetables were quite different and generally followed a sequence of root stem leaf fruit, or root leaf stem fruit. Pb and Cd contents in leafy vegetables were generally higher than those in fruits.( 3) The order of bioaccumulation factors( BFs) of heavy metals in the two vegetable types was leafy vegetables fruits. Based on fresh weight,the average BFs of Pb varied within( 0. 7—8. 4) ×10-3for leafy vegetables and( 0—0. 02) ×10-3for fruits, and those of Cd varied within( 15. 4—895. 2) × 10-3for leafy vegetables and( 0. 04—38. 1) × 10-3for fruits,which signified that the average BFs of Pb and Cd for leafy vegetables was greater than those for fruit vegetables.( 4) The correlations were not significant between the heavy metal content in vegetables and those in soils; however,total Pb and Cd in the edible parts of vegetables presented a higher significant correlation level( R2= 0. 821; n = 18,R2 0. 01= 0. 590).( 5) The results of the risk assessment on vegetables indicated that the hazard quotient( HQ) for total Pb and Cd in the edible parts of leafy vegetables were 1. 70 and 3. 73,respectively,34. 00 times and 53. 28 times higher than those of the fruits( 0. 005 and 0. 070). In relation to suitability of agricultural products in this mining area,fruits were more suitable for planting than leafy vegetables.