| Arsenic (As) pollutants have a high toxicity and can make human expose to a strongcancer risk. However some arsenic compounds have been widely used in livestockfarming, because of its advantages of promoting animals’blood circulation, stimulatinggrowth, anti-bacterial, anti-parasitic and other pharmacological effects, and then resultingin arsenic residues. And roxarsone (Rox,3-nitro-4-hydroxyphenyl arsenic acid) has beenwidely used in livestock and poultry industry as a commonly used additive in feed, but itcan hardly be absorbed in the intestine of animals, and excreted along with the feces, andthen enter into soil as organic fertilizer, affecting water and other environments.Roxarsone will be degraded to monomethylarsenic and dimethylarsenic(MMA, DMA)and inorganic arsenic species As3+, As5+, with the effect of soil microorganisms,temperature and other environmental factors, resulting in enhanced toxicity finally.Furthermore, more than75%arsenic compounds in organic fertilizer is water-soluble,having a high validity to plants; and also roxarsone is a compound which has a strongmigration, then roxarsone in soil could penetrate into the groundwater, above all,roxarsone have a great impact on the system of soil-vegetables-water.Selecting five suburban livestock farms in Shanghai as the object to study, collectedfeed, soil, vegetables, water and other samples to investigate and analysis thecharacteristic of arsenic levels in the Shanghai suburbs’surrounding environment; usedLC-HG-AFS to establish a method to detect the roxarsone in feed simultaneously, andused HPLC to establish a method to detect roxarsone in fertilizers and soil; studied thecharacteristics of roxarsone degradation and residues in soil and the effect of roxarsone onyield and total arsenic of brassica chinensis, total and inorganic arsenic of soil, enzymeactivity and microbes in soil through the field experiment. The main results were asfollows:1. In the suburbs of Shanghai, selected five large farms and surface water, feed, soiland vegetable samples were collected, and then total and inorganic arsenic would be detected to survey the current arsenic level of the livestock farms in Shanghai suburban, aswell as the usage situation of organic arsenic as feed additives. The results showed that thetotal arsenic content in the samples of water ranged from0.00to23.00μg·L-1, below thefirst standard of surface water quality (50μg·L-1); total arsenic in feed was among0.40~12.13mg·kg-1, in which inorganic arsenic was10.0%~80.0%; total arsenic inspot-checking feed samples was0.16~21.39mg·kg-1and inorganic arsenic was0.003~10.67mg·kg-1, and samples exceeding the limits of arsenic in feed accounted for16.7%; total arsenic content in soils ranged from8.08~18.50mg·kg-1, in which22.2%samples were higher than the first standard of soil environmental quality, and inorganicarsenic accounted for44.2%~78.9%of total arsenic; vegetables,total arsenic was among0.003~0.093mg·kg-1; there were some differences in different parts of the same speciesvegetables on arsenic content, and arsenic content in roots were higher than theaboveground parts; the bioconcentration factors showed a significant positive correlationwith the arsenic content in vegetables and a negative correlation with the arsenic contentin rhizosphere soil.2. The determination method of organic arsine in feed was studied by atomicfluorescence spectroscopy. In the selected experimental conditions, the detection limits ofarsanilic acid and roxarsone were respectively3.0μg·L–1and1.8μg·L–1. Thedetermination of the feed samples showed that the relative standard deviations of arsanilicacid and roxarsone were respectively0.98%and1.00%, and their average recovery rateswere respectively70.65%~101.88%and95.14%~109.82%. This method was simple andrapid in sample treatment, wide in linear range and small in matrix interference, and couldmeet the required precision in determining organic arsine residues of feed products.A high-performance liquid chromatography (HPLC) method with UV detection wasdeveloped for the determination of roxarsone in animal manure. The retention time ofroxarsone was short and it could completely avoid the interference of miscellaneous peakthrough the Symmetry ShieldTMRP18column when using the solution of0.05mol·L-1potassium dihydrogen phosphate: methanol=95:5(V/V) which containing0.1%formicacid as the mobile phase at the isocratic elution. This experiment finally chose20g·L-1K2HPO4as the extracting agent to extract the roxarsone in the manure under theultrasound conditions at60℃, and the samples were further purified by solid phase(SPE)on MAX cartridges. Its average recoveries ranged from81.14%to82.57%and relative standard deviations(RSD) less than7.0%, the coefficient of variation between0.53%and2.04%, the detection limit<20μg·L–1, what’s more, it had advantages of goodreproducibility, high precision and easy to operate. This method is applicable to detectroxarsone in manure.A high-performance liquid chromatography (HPLC) method with UV detection wasdeveloped for the determination of roxarsone in soil. The retention time of roxarsone wasshort and it could completely avoid the interference of miscellaneous peak through theSymmetry ShieldTMRP18column using the solution of0.05mol·L-1potassium dihydrogenphosphate:methanol=95:5(V/V) which containing0.1%formic acid as mobile phase at theisocraticelution; this experiment had compared the efficiency of three different extractingagents in extracting the roxarsone in soil under two different extracting methods, andfinally got the best method to detect roxarsone in soil which chose0.1mol·L–1NaH2PO4:0.1mol·L–1H3PO4=9:1(V/V) as the extracting agent under theultrasound conditions at60℃, and then evaporated the extracts to be almost dryness byapplying the rotary evaporator and subsequently redissolved in deionized water. Itsaverage recoveries ranged from83.58%to93.47%and relative standard deviations(RSD)less than7.0%, coefficient of variations<2%, the detection limit<20μg·L–1, what’s more, ithad advantages of good reproducibility, high precision and easy to operate. This method isapplicable to detect roxarsone in soil.3. In this field experiment, different levels of organic fertilizer which containroxarsone were applied on brassica chinensis to examine the roxarsone residue and theeffect of roxarsone on yield and total arsenic of brassica chinensis, and the effect on totalarsenic, inorganic arsenic, enzyme activity and microorganisms in soil. The results showedthat:(1) With the treatment of organic fertilizer which contain roxarsone, yield reducedfirst and then raised, and in the concentration of100kg·hm-2, it got the minimum with68percent of the control treatment; the amount of arsenic in brassica chinensis became higherwith increasing organic fertilizer which contain roxarsone and extending the time ofplanting within30days，and the highest concentration was2.05mg·kg-1; the arsenic levelof brassica chinensis was elevated at first and then declined after45days, increasingsignificantly at5000kg·hm-2of organic fertilizer which contain roxarsone and having asignificantly difference compared with other treatment groups.(2) The total arseniccontent in soils showed a trend of increase and then decrease with the extension of planting, however, inorganic arsenic increased at first and then stabilized, and the highestpot of total arsenic content in soils was12.00mg·kg-1and the proportion of inorganicarsenic in total arsenic was69.54%~72.32%.(3) After30days, there was a certainpositive correlation coefficient between the total arsenic content in brassica chinensis andsoils, and also the bioconcentration factor of brassica chinensis was significantlypositively correlated with the arsenic levels in vegetables and soils.(4) Roxarsoneeliminated relative slowly in the soil which vegetables grown in, and some roxarsone stillresidue in the soil after45days when the amount of organic fertilizer which containroxarsone was higher than5000kg·hm-2, and the concentration was19.11mg·m-3.(5) Withthe increase of organic fertilizer which contain roxarsone, the activity of urease enzyme insoil showed a slowly rising trend and the maximum value was0.973mg NH3-H·(24h·gsoil)-1; there was an inhibition on neutral phosphatase enzyme activity, and the least pointwas0.899mg hydroxyl benzene·(24h·g soil)-1; catalase enzyme activity was increasingand then downward with increasing roxarsone levels in soil, getting the top1.394mL(0.1mol·L-1KMnO4)·(h·g soil)-1.(6) The amount of bacteria became higher whenincreasing the amount of organic fertilizer which contain roxarsone in soil and there had asignificantly difference between the treatment groups, however, the amounts of fungi andactinomycetes showed a trend of decline first and increase second. |
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