Bioavailability Of Cd/Pb In Soil To Chicken

Heavy metal contaminated soil can be accidentally ingested by the animals（including human being）,heavy metals in the soil then enter the circulatory system through the digestive system and eventually accumulate in various tissues and organs,as the accumulation increases,the heavy metals may endanger animal health.Free-range chickens in contaminated areas can ingest contaminated soil,studies have shown that free-range chickens can ingest up to 10%or more soil in their food.However,there is a lack of research on the bioavailability of heavy metals in contaminated soil to chicken and the distribution of heavy metals in chicken organs after ingestion of contaminated soil.Therefore,in this study,chickens were fed with different levels of cadmium(Cd at 10,20 and 80 mg kg^-1),lead(Pb at 100,200 and 500 mg kg^-1)and contaminated soil(soil ratios at 3%,5%,10%,20%and 30%,total soil Cd and Pb were 105and 4840 mg kg^-1,respectively)for 23 days.After that,the heavy metal concentrations in chicken tissues/organ were determined to estimate the bioavailability of heavy metals in contaminated soil on chickens.The main findings of the study were as follows:1.Cadmium and lead in the feed inhibited the growth of chickens.At the end of the experiment,the average chicken body weight of the highest level cadmium and lead treatments were 0.83 and 0.84 times that of the control,and 0.69 times that of the control at the highest rate of soil-spiking in feed.The feed Cd-spiking significantly increased（p<0.05）the concentrations of Cd in liver,kidney and gizzard,while lower concentrations of Cd were found in femur,heart,breast and drumstick,and the strongest linear correlation was found for Cd between the concentrations of cadmium in kidney and the dose of cadmium in feed（p<0.001）.The feed Pb-spiking significantly increased（p<0.05）the Pb concentrations in chicken liver,kidney,femur and gizzard,with lower levels in the heart,breast and drumstick of the chicken.The strongest correlation（p<0.001）between the lead concentrations and the dose of lead in the feed was found in the femur.Both antagonistic and synergistic effects between Cd and Pb were observed in the study.Lead concentrations in liver,kidney and gizzard were lower when30%soil was spiked to the feed than 20%,indicating that the feed Pb concentrations were too high to be effectively absorbed in the 30%treatment.The maximum concentrations of gizzard Cd and Pb were 21.6 and 123 mg kg^-1,respectively,which implies the potential use of gizzard as an endpoint for evaluating the bioavailability of Cd and Pb in chickens.For free-range chickens from Cd and Pb contaminated areas,it is recommended not to consume their liver,kidney and gizzard.2.In this study,three methods were used to calculate the Cd/Pb bioavailability in soil,namely,Method I,dose normalized metal concentration（DNMC）ratio method,where the bioavailability is calculated as the ratio of DNMC of soil-spiked treatment to DNMC of Cd/Pb reagent-spiked treatment;Method II,dose response curve（DRC）method,where the bioavailability is calculated as the ratio of DNMC of soil-spiked treatment to slope of dose response curve（DRC）of Cd/Pb reagent-spiked treatments;Method III,slope/slope method,the bioavailability is the ratio between the slopes of the DRC of soil-spiked treatment and that of DRC of reagent-spiked treatments.The results showed that except cadmium bioavailability in femur,the bioavailability values were less than 100%.The ranges of Cd bioavailability for method I,II and III were 47.6-69.1%,49.4-67.4%and 48.7-72.3%,respectively,with mean values of 59.2,57.8 and 62.0%,respectively.For lead bioavailability,most data of bioavailability were less than 100%.The ranges of bioavailability of lead for method I,II and III were 61.3-76.1%,68.2-113%and 46.4-71.7%,respectively,and the mean values were 66.3,84.9 and 58.8%,respectively.The distribution mechanism and bioavailability of heavy metals in chicken tissues/organ under the ingestion of heavy metal contaminated soil by chickens should be further investigated in future works.3.Studies on the bioaccessibility of heavy metals in organs obtained from chickens fed feeds with different treatments showed that the bioaccessibility of cadmium in liver,kidney and gizzard ranged from 10.6-17.5%,7.73-12.5%and 5.81-21.6%in the gastric phase,respectively,and from 13.5-43.0%,9.45-15.6%and 7.36-16.1%in the intestinal phase,respectively.The bioaccessibility ranges for Pb in liver,kidney and gizzard were 20.2%-50.7%,9.42%-23.1%and 6.96%-8.19%in the gastric phase and 55.5%-71.4%,24.5%-37.4%and19.7%-27.4%in the intestinal phase,respectively.The chicken tissues/organ showed high metal bioaccessibility at low of Cd and Pb concentrations and low bioaccessibility at high concentrations of Cd and Pb.The above results indicate that chickens can absorb heavy metals from contaminated soil.Free-range chicken farm should be strictly prohibited in soil heavy metal contaminated areas.