Heavy metals in meats
Total 1066 meat samples including 511 pork samples, 250 chicken, 184 beef, 74 duck, and 47 mutton purchased from local markets of Zhejiang were analyzed in this study. As shown in Table 2 and Table 3, average levels of As, Cd, Cr, Cu, Hg, Ni, and Pb were 0.018, 0.002, 0.061, 0.801, 0.0038, 0.055, and 0.029 mg/kg wet weight respectively. Based on the Chinese National Food Safety standard 27, the maximum allowable concentrations (MAC) of As, Cd, Cr, Hg and Pb in meat in China were 0.5, 0.1, 1, 0.05 and 0.2 mg/kg. The number of sample exceeding the MAC is 1 for As, 2 for Hg and 10 for Pb. Our results were similar with those found in Beijing China, where there are Cr (0.573 mg/kg), Cd (0.015 mg/kg), Pb (0.167 mg/kg), As (0.053 mg/kg), Hg (0.018 mg/kg) in meats (pork, beef, mutton, chicken) 28. In some potential polluted areas, average level of heavy metals, such Cd and Pb were more than 0.2 mg/kg in meat product 29, 30.
Different animal species may have different bio-accumulation ability for heavy metals. The average levels of As, Cd, Cr, Cu, Hg, Ni, and Pb in different meat samples were shown in Figure 2. Compared with beef, chicken, duck and pork, mutton had relative lower levels of As, Cd, and Cr (P<0.05). High Cu concentration (average 3.1 mg/kg) was found in duck meat. Considering the nearly 80% water content in duck meat, our result was similar with the report of Aendo et al. 31, who found duck meat with 15.28 mg/kg dry weight for Cu in Thailand. For Hg, Ni, and Pb, there was no significant difference among five targeted meats (P <0.05). Furthermore, 4 of 248 chicken muscle samples contained Pb with levels above the safety threshold of 0.2 mg/kg (fresh weight). The ratio of over-limit was lower than that reported in Guangzhou, China where 2 of 63 muscle samples had Pb contents exceeding this limit 32. The Cd (0.002 mg/kg) in beef was lower than report of Hashemi 33 who found 0.28 mg/kg Cd in Iran.
Pearson correlation analysis (Table 4) showed that there were significant positive correlations for Cd-Hg (r=0.9141, P<0.05), Pb-Hg (r=0.98837, P<0.05) and Cd-Pb (r=0.9504, P<0.05) in meat samples. Negative correlations in Cu-Cd (r= -0.6515, P<0.05) and Cu-Pb (r= -0.6101, P<0.05) were found in our results. We suppose that two groups of Cd-Hg-Pb and Cu were accumulated by different sources. Actually, most of livestock and poultry in Zhejiang were farming with artificial feeds which may be the main source of heavy metals. The contamination incidence rates of harmful elements, such as Cd, Hg, Pb, and As in feedstuffs and feeds were high, and feeds were most often contaminated with Cr, followed by As, Cd, and Hg 9. The mean As contents of chicken feeds collected in Jiangsu province of southern China was reported to be 0.13 mg/kg 34 while the total contents of As in poultry feeds in northeastern China varied from 0.02 to 6.42 mg/kg 35. Previous studies showed that Cu was typically present at levels 2 to 8 times higher than the required ones in poultry and livestock feeds in China 34, 35. As we known, compounds containing Cu element were commonly used as a growth promoter in diets of poultry, especial duck 36.
Exposure assessment and health risk
According to the data of food consumption survey 23, the estimated livestock and poultry meat intake was 112.9 g/day/person. The recommended reference doses (RfDs) or safe values were based on previous reports 30, 32. The mean and high exposure was presented by the average and P97.5 elements levels， respectively. As shown in Table 4, mean exposure doses of As, Cd, Cr, Cu, Hg, Ni, and Pb by meat consumption were0.034, 0.004, 0.115, 1.507, 0.007, 0.103, and 0.055 μg/kg bw/day. And high exposure values were 0.207, 0.024, 0.598, 7.696, 0.047, 0.790, and 0.339 μg/kg bw/day. Our mean exposure data (As, Cd, Cr, Hg and Pb) were lower than those reported in Beijing, China 28.
To appraise the health risk associated with these metals, targeted hazard quotient (THQ) was calculated by dividing daily intake of elements by their reference doses. Hazard index (HI) combined all THQs was adopted to assess the total health risk 37, 38. An HI more than 1 is considered as not safe for human health. As shown in Table 5, all THQs were less than 1. Both mean and P97.5 HIs were no more than 1. HI for P97.5 level presented as the high exposure was 0.768. It indicated that there was low health risk to exposure of common toxic elements by intake of these meats. However, it should be noticed that other potential exposure pathways for foods, such as vegetables, cereals, fruits, and fish might be considered except for livestock and poultry meats.