Fate of arsenic compounds in poultry litter upon land application

The use of the organic As compound, roxarsone, as an antibiotic additive to poultry feed continues to raise concern over potential negative environmental impacts. Total As concentration in poultry litter can reach >40 mg kg⁻¹ and both roxarsone and its mineralization product As(V) have been identified in poultry litters (PL). To investigate the fate of these As species upon land application of PL we conducted two studies. In the first, an Orangeburg soil (Ultisol from the Atlantic Coastal Plain) was spiked with either 20 mg kg⁻¹ As(V) or roxarsone and incubated at 10% moisture content for 4 months. Exchangeable As was determined periodically by extraction with 0.1 M PO₄. Both As(V) and roxarsone displayed similar desorption; initially, approximately 70% of added As was ligand exchangeable and this decreased to 35% after 4 months incubation, presumably due to either slow sorption reactions or a change in solid phase speciation of As to less exchangeable forms. In the second study, various manipulations of two PL samples were applied to the Orangeburg soil at realistic field application rates. The treatments were wet to 10% moisture content and water soluble As, Cu and organic carbon (DOC) was measured over 30 days. Arsenic and Cu solubility were highest from the dried litter samples. Ashing of the PLs decreased soluble As and Cu, presumably because of the loss of organic matter from the ashed litter and subsequent decrease in DOC. Application of leachates from either PL resulted in higher concentrations of soluble As and Cu than when the soil was amended with equivalent concentrations of soluble As and Cu dissolved in DI H₂O. We hypothesize that the increased levels of DOC from the PL treatments enhance As and Cu solubility through competitive sorption and complexation, respectively. In fact, As and Cu solubility was correlated to DOC levels in the amended soil extracts. Even though land application of PL introduced relatively low concentrations of As and Cu to soil it appeared that other soluble constituents of PL significantly enhanced As and Cu solubility.     

The role of organic and inorganic substituents of roxarsone determines its binding behavior and mechanisms onto nano-ferrihydrite colloidal particles

The retention and fate of Roxarsone (ROX) onto typical reactive soil minerals were crucial for evaluating its potential environmental risk. However, the behavior and molecular-level reaction mechanism of ROX and its substituents with iron (hydr)oxides remains unclear. Herein, the binding behavior of ROX on ferrihydrite (Fh) was investigated through batch experiments and in-situ ATR-FTIR techniques. Our results demonstrated that Fh is an effective geo-sorbent for the retention of ROX. The pseudo-second-order kinetic and the Langmuir model successfully described the sorption process. The driving force for the binding of ROX on Fh was ascribed to the chemical adsorption, and the rate-limiting step is simultaneously dominated by intraparticle and film diffusion. Isotherms results revealed that the sorption of ROX onto Fh appeared in uniformly distributed monolayer adsorption sites. The two-dimensional correlation spectroscopy and XPS results implied that the nitro, hydroxyl, and arsenate moiety of ROX molecules have participated in binding ROX onto Fh, signifying that the predominated mechanisms were attributed to the hydrogen bonding and surface complexation. Our results can help to better understand the ROX-mineral interactions at the molecular level and lay the foundation for exploring the degradation, transformation, and remediation technologies of ROX and structural analog pollutants in the environment.     

洛克沙胂暴露胁迫对土壤微生物群落结构特征的影响

采用磷脂脂肪酸(phospholipid fatty acid,PLFA)方法,分析了洛克沙胂残留对土壤微生物群落结构的影响特征。结果表明,在整个采样周期中,每克土壤总PLFA含量在洛克沙胂胁迫影响下出现明显降低,且存在一定的剂量依赖效应。经主成分分析,第1周,洛克沙胂低浓度组(w=15 mg·kg-1)土壤微生物群落结构和对照组差异不明显,第2、3、5、8周,各组土壤微生物群落结构多样性的类型差异显著,其中高浓度组(w=150 mg·kg-1)与对照组差异最大。结果表明,洛克沙胂可致土壤微生物群落结构多样性改变,暴露浓度越高其作用越强。同时,洛克沙胂对土壤微生物群落结构多样性的影响还表现出时间差异,在暴露胁迫的后期(第5、8周),洛克沙胂的影响逐步减弱,可能与洛克沙胂在土壤中发生化学结构改变和降解有关。     

Impact of roxarsone on the UASB reactor performance and its degradation

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, ROX) has been widely used for decades as an organoarsenic feed additive to control intestinal parasites and improve feed efficiency in animal production. However, most of the ROX is excreted into the manure, causing arsenic contamination in wastewater. The arsenic compounds are toxic to microorganisms, but the influence of continuous ROX loading on upflow anaerobic sludge blanket (UASB) reactor is still unknown. In this study, the impact of ROX and its degradation products on the performance of the UASB reactor and the degradation and speciation of ROX in the reactor were investigated. The UASB reactor (hydraulic retention time: 1.75 d) was operated using synthetic wastewater supplemented with ROX for a period of 260 days. With continuous ROX addition at 25.0 mg·L^–1, severe inhibition to methanogenic activity occurred after 87 days operation accompanied with an accumulation of volatile fatty acids (VFAs) and a decline in pH. The decrease of added ROX concentration to 13.2 mg·L^–1 did not mediate the inhibition. As(III), As (V), MMA(V), DMA(V), HAPA and an unknown arsenic compound were detected in the reactor, and a possible biotransformation pathway of ROX was proposed. Mass balance analysis of arsenic indicated that 60%–70% of the arsenic was discharged into the effluent, and 30%–40% was precipitated in the reactor. The results from this study suggest that we need to pay attention to the stability in the UASB reactors treating organoarsenic-contaminated manure and wastewater, and the effluent and sludge from the reactor to avoid diffusion of arsenic contamination.

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洛克沙胂在青菜及土壤中的残留及降解特性

通过向土壤中施加含洛克沙胂有机肥的田间试验,研究有机肥中的洛克沙胂在土壤-蔬菜中的降解、迁移转化及残留.结果表明,土壤中施加低浓度的洛克沙胂对青菜的生长具有一定的抑制作用,相比于对照组减产15%~32%;青菜对土壤中砷具有一定的富集作用,且其根部为砷主要蓄积部位;土壤中总砷含量与施入洛克沙胂的量成正相关,并且随着种植时间的延长先升高再下降,最高达12.94 mg·kg-1,土壤无机砷含量随着种植时间的延长先升高并于30 d后趋于稳定,占总砷的66.75%~98.56%;青菜中总砷含量与土壤总砷含量及青菜砷富集系数之间均存在一定的正相关;洛克沙胂在土壤中的降解速率缓慢,含洛克沙胂有机肥量添加量高于5 000 kg·hm-2时,45 d后土壤中有洛克沙胂残留;施入一定量的洛克沙胂能显著提高土壤中细菌的数量,对于霉菌和放线菌的生长,较低浓度的洛克沙胂具有一定的抑制作用,较高浓度的洛克沙胂具有一定的促进作用.     

高效液相色谱法测定地下水中洛克沙胂

地下水水样经磷酸二氢钾提取后,用MAX固相萃取小柱对其净化、浓缩,再用高效液相色谱仪测定样品中的洛克沙胂。对色谱条件进行优化,使该方法在0.500 mg/L~10.0 mg/L范围内线性良好,方法检出限为0.047μg/L。空白加标样6次测定结果的RSD为5.3%,空白水样的3个质量浓度水平的加标回收率为79.8%~88.8%。将该方法用于测定6个地下水实际样品中洛克沙胂,其中1个被检出,测定值为0.42μg/L。