The Study on Migration,Transformation and Risk Assessment of Arsenic Bearing in Fodder Among Chicken-Soil-Vegetable System
Author:Xie Hai Zuo
Supervisor:wang wen hua
Arsenic is a kind of metalloid elements.Arsenic have several species,like inorganic arsenic(As(V)and As(III))and organic arsenic(methyl arsenic(MMA)and dimethylarsenic(DMA).Organic arsenic compounds can significantly promote poultry growing,against intestinal parasitic diseases and increase egging rate,which had been widely used in poultry industry.Poultry can absorbe little arsenic with tissues,most of them were amended with litter into the soil environment,leading different species of arsenic migration in the soil-plant system.In this paper,chicken fodders,chicken and their tissues,poultry litter and soil surrounding the poultry farm from 35 intensive poultry farms with vegetables in Pudong district of Shanghai were sampled,and their arsenic concentration were analyzed.Also,the mechanism of transformation between different forms of arsenic were discussed in the soil amended with poultry litter.Under laboratory conditions,adding different concentration of pourltry litter into the soil by different cultivation way and its effect on germination rate and growth of the oilseed rape were observed.In this paper,the health risk on the human body through the soil and dietary intake of chicken and vegetables intake were evaluated.Variation trend for ecological risk assesment in soil and health assesement on human body by intake of chicken with the change of arsenic content in fodder were also analysed.Scientifically evaluating results on the risk of arsenic in the fodder-chicken – soil-vegetable system provide the basic data and scientific guidance for governance standards of contaminated soil for our country.The main research results were as followed:(1)Different chicken tissues have different arsenic concentrations,with the order of: chicken intestine(1.84±0.57)>chicken liver(1.11±0.57)>chicken(0.70± 0.29)>chicken lung(0.70±0.29)>egg(0.08±0.03),mg/kg.The arsenic content in those tissues exceeded the limit of arsenic in food hygiene standard(0.5mg/kg or less)in our country except the eggs.The determination results for different chicken age of fodder with brand indicated that the roxarsone was found in the fodder for the chicken laying eggs.(2)In the process of soil amended with poultry litter aging under the condition of anaerobic circumstances showd that the inorganic arsenic concentration in the experimental group of AN10 and AN60 decreased to different extent during the beginning 7 days,and the concentration of organic arsinic DMA raised;From 30 days to 110 days remained relatively stable throughout the aging experiments for all arsenic species,which means the soil environment achieved was relatively stable and balanced.In the process of soil amended with poultry litter aging under the condition of aerobic circumstances showd that the As(V)in AE10 and AE60 fell 65.13% and 51.55%,respectively in the earlier 6 days,and the arsenic species remained relatively stable in 7-30 days;Methyl arsenic substances(MMA and DMA)in 0-15 days,has experienced a steady upward trend,show that the transformation of arsenic species effectted by the form of biological and non-biological factor under the aerobic environment.The total As for the soil amended with poultry litter uner anaerobic and aerobic environment decreasd 7.45%和 19.05 % by the end of aging,respectively,which indicated that the arsenic in soil was transformed to volatile by the form of methylated-arsenials.The calculation results on the quantum chemical and thermodynamics on Gibbs free energy in gaseous and liquid phase was discussed.The calculation of Gibbs free energy in liguid phase for methylated reaction of arsenic implied that the ΔG<0 for all kinds of organic arsenic,which indicated reaction can be proceed spontaneously.It is implied that the calculation of Gibbs free energy on methylated-reduced course for kinds of arsenic is decreased with the higher methlation in this order :As(V)>MMA(V)>DMA(V)>TMA(V)。 The results may be correlated with the repulsive force around the atom.The calculation of Gibbs free energy on methylated-reduced course for kinds of arsenic spontaneously reaction is in this order: As(III)<MMA(III)<DMA(III).(3)With the growing quantity of poultry litter amend to soil,the germination rates of oilseed rape and its growth had more significant inhibition.The relationship between germination rate and negatively correlated with the concentration of the MMA(r=0.63,p <0.05).For the 10% treatment,the length of root and stem leaf of oilseed rape decreased 44.27% and 44.27% respectively;For the 40% treatment contrasted with the control group,the biomass of root and stem is 1/3 and 1/4,respectively.The total As in the stem of oilseed rape showed positive correlation with the content of As(III)(r=0.516,p<0.05)and DMA(r=0.601,p<0.01)in soil,respectively.The BFs of the root for control group and 5% treatment were 0.61±0.34 and 0.79± 0.24,which were greater than 1 for the treatment percent exceeded 5%.The TFs of stem for oilseed rape is less than 0.1,The TFs of root is 24-37 times higher than that in stem.The results indicated that the stem of oilseed rape can absorbe little arsenic but easily accumulated in the root,few of arsenic could be transported to the ground part.(4)The ecological risk based on the content of arsenic species in the soil were evalutated,and which were contrast with the ecological risk model based on the total arsenic(i.e.,Nemerow Index method,geoaccumulation index method and index of Hakanson’s ecological harm).The results showed that ecological risk based on the content of arsenic species in the soil behaved more accuracy and sensitivety.(5)For the health risk assessment with the exposure levels of intake 0.5kg chicken meat,0.01 kg chicken lung,liver and intestine and 0.35 kg egg per week,respectively,the results showed that the noncarcinogenic risk of the adult is in the following order: meat(1.19±0.50)>intestine(0.31±0.10)>liver(0.19±0.10)>egg(0.19±0.07)>lung(0.10±0.05).For the carcinogenic risk,the risk of meat,lung,liver,intestine and eggs were 5.35E-05±2.23E-05 、 4.66E-06±2.23E-06 、 8.49E-06± 4.37E-06 、1.40E-05±4.37E-06 and 8.68E-06±3.26E-06,respectively,which were all in the acceptable range between1.0E-06~1.0E-04.Among them,the risk value of dietary intake of chicken meat was obviously higher than other tissues.For the health risk assessment with the exposure levels of intake 1kg oilseed rape and Chinese rape per week,respectively,the results showed that the noncarcinogenic risk for the adult and adolescent were low,the average value was 0.29±0.23 and 0.36±0.29,respectively,which are less than 1 of health standard values;However,the carcinogecin risk for children was 1.36±1.10,which could be greater than the health standard limit of 1.The risk of intake the root of rape was greater two orders of magnitude than the risk of intake the stem of rape for the noncarcinogenic risk,and the risk of intake rape increase with the raised poultry litter proportion in the soil.For the carcinogenic risk for intake of Chinese rape for adults,adolescent and children were 1.31E-05±1.06E-05、1.61E-05±1.30E-05 and 6.12E-05±4.93E-05,respectivley,which exceeded the lower limit of 1.0E-06 and showed that certain health risk might occurred to the human body by long-term intake.The risk of stem intake was significantly lower than the risk of root intake for rapeseed concerned with the carcinogenic,the value of the former one was about a quarter of value of the later one.The variation trend for non-carcinogenic risk and carcinogenic risk of chicken tissues and the variation trend for Ecological risk assesment in soil with the change of arsenic content in fodder indicated that the non-carcinogenic risk increase significantly by intake of chicken tissues when the arsenic content in fodder is higher than 10mg/kg,and the soil will be suffer sight pollution when the arsenic content in fodder distributed between 3~25mg/kg.