中国粮食主产区耕地土壤重金属时空变化与污染源分析

土壤重金属污染威胁着农田生态系统安全和人类健康.基于2000年以来中国五大粮食主产区3 006个耕地样点的土壤重金属实测数据和20世纪80年代的土壤重金属历史数据,采用单因子指数法评估了粮食主产区耕地土壤重金属的污染现状和变化趋势,并基于地累积指数,结合区位环境污染探讨了其污染来源.结果表明,中国粮食主产区耕地土壤重金属点位超标率为21.49%,整体以轻度污染为主,其中轻度、中度和重度污染比重分别13.97%、2.50%和5.02%.四川盆地、长江中游及江淮地区、黄淮海平原、松嫩平原和三江平原的耕地点位超标率分别为43.55%、30.64%、12.22%、9.35%和1.67%,南方耕地污染重于北方.主要污染物为Cd、Ni、Cu、Zn、Hg,超标率分别为17.39%、8.41%、4.04%、2.84%、2.56%.自20世纪80年代以来,耕地土壤重金属含量呈增加趋势,整体上点位超标率增加了14.91%,其中Cd、Ni、Cu、Zn和Hg的污染比重分别增加了16.07%、4.56%、3.68%、2.24%和1.96%.除三江平原外,其他4个粮食主产区耕地土壤重金属点位超标比重增加趋势显著,且南方地区的Cd、Ni和Cu重金属超标比重变化量高于北方,而Hg和Cr增速低于北方.Cd、Hg以人为污染源为主,其他6种重金属以自然污染源为主,但Pb、Zn和Cu约有20.00%的点位受人为活动的影响.矿业、工业、污灌水是主要的污染源,除污灌水来源北方重于南方外,其余污染来源均是南方污染重于北方,污染物种类也多于北方.     

Pb和Cd赋存形态与土壤理化性质相关性研究

选择我国14种具有代表性的重金属污染土壤,测定其主要理化性质（pH、阳离子交换量、有机质、粉粒和黏粒）,采用改进的BCR顺序提取法对其中的Pb和Cd进行形态分析,运用SPSS 20.0软件进行Pearson相关性分析,建立逐步回归模型,研究重金属赋存形态与理化性质的相关性。结果表明,Pb和Cd的酸可溶态与pH值呈极显著负相关,相关性系数r分别为-0.80和-0.78,与阳离子交换量呈显著正相关,r分别为0.54和0.61,与有机质、粉粒和黏粒无相关性;Cd的可还原态与有机质呈显著正相关,r=0.56,与其它理化性质无相关性;可氧化态与有机质和黏粒呈显著正相关,与其它理化性质无相关性;残渣态与主要理化性质均无显著相关性。由逐步回归模型发现,酸可溶态、可还原态、可氧化态与理化性质回归效果均较好。     

长期不同施肥对稻田土壤有机碳矿化及激发效应的影响

通过室内模拟培养实验,结合14C同位素标记技术,研究了不施肥(CK)、单施化肥(NPK)、秸秆还田+化肥(ST)这3种施肥处理下稻田耕层土壤有机碳矿化特征及其对添加外源葡萄糖的响应特征.结果表明,56 d培养实验结束时,CK处理土壤累积矿化率(土壤原有有机碳累积矿化量/土壤总有机碳含量)达到1. 64%,而NPK和ST处理较CK处理显著降低了0. 34%和0. 39%(P 0. 05),表明长期施肥对土壤碳有一定的固持作用.长期不同施肥处理土壤对添加外源葡萄糖的响应有所不同,表现出了不同程度的激发效应.随着培养时间的推移,3种处理土壤碳矿化的激发效应由负激发效应逐渐转为正激发效应. 56 d时,ST和NPK处理土壤的负累积激发效应比CK分别显著提高了22. 07和9. 05倍(P 0. 05).结构方程模型分析表明,土壤NH+4-N和DOC含量主要通过影响土壤MBC和MBN含量间接影响土壤累积激发效应,且NH+4-N对土壤累积激发效应有直接的显著负影响.综上所述,长期施肥降低了稻田土壤原有有机碳累积矿化率,有利于增强稻田土壤碳的固持和积累,秸秆还田加化肥效果更加明显.     

微囊藻毒素MC-RR在农田土壤中吸附行为研究

采用批处理实验研究了典型微囊藻毒素MC-RR(10~400μg·L-1)在农田土壤(水稻土、赤红壤和咸田土)中的吸附动力学和热力学特征,并探讨土壤理化性质对其吸附行为的影响.结果表明,MC-RR在农田土壤中的吸附均于4 h内达到平衡,吸附动力学均符合拟二级动力学方程(R20.994),液膜扩散是主要控速过程;各温度下(15、25、35℃)MC-RR吸附等温线均符合Langmuir方程(R20.827).水稻土吸附MC-RR主要为自发放热的物理吸附过程,其吸附能力随温度升高而降低;赤红壤和咸田土吸附MC-RR主要为自发吸热的化学吸附过程,其吸附能力随温度升高而增强.土壤粘粒矿物和有机质含量显著影响其对MC-RR的吸附能力,粘粒矿物含量越高,有机质含量越低,MC-RR吸附能力越强.MC-RR在有机质含量较高的水稻土中难吸附,而在有机质含量较低的赤红壤和粘土含量较高的咸田土中易吸附.     

填埋场底土污染物浓度实测值和理论解的比较

为了研究现场条件下污染物在粘性土中的运移机理,对运行13年的苏州七子山填埋场进行了钻孔取样.通过对土样进行分层切片、加去离子水混合并结合室内小型离心机分离,得到了填埋场底土中Cl-,Na+及COD的孔隙水浓度.将室内试验测试值和一维扩散理论进行了比较,结果表明,实测浓度剖面与扩散曲线差别较大,可见水力梯度引起的对流和机械弥散作用比分子扩散作用来得重要.将实测值与一维对流弥散解析解的计算值亦进行了比较,结果表明试验数据较为发散,但可以采用一维对流弥散理论进行大致的拟合,从而可得到运移参数的取值范围.进一步的理论预测表明,当填埋场运行30年之后,Cl-的影响深度可达到10 m以上.为了防止和延缓渗滤液污染物的进一步运移,填埋场应采取有效措施阻止渗滤液的扩散.     

Sorption of imidacloprid and its metabolites on tropical soils

Abstract

The sorption of imidacloprid (l‐[(6‐chloro‐3‐pyridinyl)‐methyl]‐N‐nitro‐2‐imidazolid‐inimine) (IMI) and its metabolites imidacloprid‐urea (l‐[(6‐chloro‐3‐pyridinyl)‐methyl]‐2‐imidazol‐idinone) (IU), imidacloprid‐guanidine (l‐[(6‐chloro‐3‐pyridinyl)‐methyl]‐4,5‐dihydro‐lH‐imidazol‐2‐amine) (IG), and imida‐cloprid‐guanidine‐olefin ( 1 ‐[(6‐chloro‐3‐pyridinyl)methyl]‐lH‐imidazol‐2‐amine) (IGO) was determined on six typical Brazilian soils. Sorption of the chemicals on the soil was characterized using the batch equilibration method. The range and order of sorption (Kd) on the six soils was IG (4.75–134) > IGO (2.87–72.3) > IMI (0.55 ‐16.9) > IU (0.31–9.50). For IMI and IU, Kd was correlated with soil organic carbon (OC) content and CEC, the latter due to the high correlation between OC and cation exchange capacity (CEC) (R²=0.98). For IG and IGO, there was no correlation of sorption to clay, pH, OC or CEC due to the high sorption on all soils. Average Koc values were IU = 170, IMI = 362, IGO = 2433, and IG = 3500. Although Kd and Koc values found were consistently lower than those found in soils developed in non‐tropical climates, imidacloprid and its metabolites were still considered to be slightly mobile to immobile in Brazilian soils.     

Fertility status and management implications of wetland soils for sustainable crop production in Akwa Ibom State, Nigeria

Fertility status of soils of three wetland types in Akwa Ibom State, Nigeria, was investigated. The wetland types are Inland Valley (IV), Flood Plain (FP) and Mangrove (MG). The soils have silt-clay ratios above 0.15 and 0.25 indicating that they are of young parent materials with low degree of weathering and possible weatherable minerals for plant nutrition. The pH of the soils was near neutral (>6.4) when wet but extremely acid (>3.5) when dried indicating that the soils are potential acid sulphate soils. Organic matter content was high with mean values of 12.59, 6.03 and 3.20% for IV, FP and MG soils, respectively. Total N (nitrogen) was low except in IV soils where the value was above the 0.30% critical level. The C:N ratios were narrow with mean of 20.90, 12.17 and 12.12 for IV, FP and MG soils, respectively. The contents of basic cations [Calcium (Ca), Magnesium (Mg), Potasium (K) and Sodium (Na)] were low while acidic cations [Aluminium (Al) and Hydrogen (H)] were high. The Ca:Mg ratios were below the optimum range of 3:1 to 4:1 required for most crops. The Mg:K ratios were above 1.2, below which yields of crops like corn and soybean may be reduced. Effective cation exchange capacity (ECEC) was below the 20 cmol/kg. Percent base saturation was low (<38) indicating that the soils are potentially less fertile. Exchangeable Al and percent Al saturation were high, above 60% in IV and FP soils. Electrical conductivity was above the critical value of 2 dsm⁻¹ while exchangeable sodium percentage was less than 15. Available Phosphorus (P) and low, <10 ppm and free Fe₂O₃/clay ratios were <0.15. Positive correlation existed between silt and ECEC, implying that silt contributed to nutrient status of the soils. Generally, fertility status of the soil is low and would require maintenance of adequate organic matter, application of lime and organic and inorganic fertilizers, drainage and irrigation if the land is to be used for intensive/sustainable crop production. Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue.     

High-resolution inventory of NO emissions from agricultural soils over the Ile-de-France region

Arable soils are a significant source of nitric oxide (NO), a precursor of tropospheric ozone, and thereby contribute to ozone pollution. However, their actual impact on ozone formation is strongly related to their spatial and temporal emission patterns, which warrant high-resolution estimates.Here, we combined an agro-ecosystem model and geo-referenced databases to map these sources over the 12 000 km² administrative region surrounding Paris, France, with a kilometric level resolution. The six most frequent arable crop species were simulated, with emission rates ranging from 1.4 kg N-NO ha⁻¹ yr⁻¹ to 11.1 kg N-NO ha⁻¹ yr⁻¹. The overall emission factor for fertilizer-derived NO emissions was 1.7%, while background emissions contributed half of the total NO efflux. Emissions were strongly seasonal, being highest in spring due to fertilizer inputs. They were mostly sensitive to soil type, crops' growing season and fertilizer N rates.     

Sorption behavior of bensulfuron-methyl on andisols and ultisols volcanic ash-derived soils: Contribution of humic fractions and mineral-organic complexes

Bensulfuron-methyl sorption was studied in Andisol and Ultisol soils in view of their characteristic physical and chemical properties, presenting acidic pH and variable charge. Humic and fulvic acids (HA and FA) and humin (HUM) contributions were established. Sorption was studied by using two synthetic sorbents, an aluminum-silicate with iron oxide coverage and the same sorbent coated with humic acid. Freundlich model described Bensulfuron-methyl behavior in all sorbents (R² 0.969-0.998). K_f for soils (8.3-20.7 μg^1−1/n mL^1/n g⁻¹) were higher than those reported in the literature. Organic matter, halloysite or kaolinite, and specific surface area contributed to the global process. The highest K_f for HA, FA and HUM were 539.5, 82.9, and 98.7 μg^1−1/n mL^1/n g⁻¹. Model sorbents described the participation of variable charge materials with high adsorption capacity. The constant capacitance model was used to assess effects of Bensulfuron-methyl adsorption on the distribution of SOH, SOH₂⁺ and SO⁻ sites of sorbents.     

Incorporating uncertainty in a chemical leaching assessment

Pesticide leaching models are being used to assist in the regulation and management of pesticides by indicating their potential for leaching to groundwater. Uncertainty in model input data is not, regrettably, included in most pesticide leaching assessments. In the work described here, we use logarithmic transformations of the attenuation factor (AF), a simple process-based index model, to represent uncertainty in a pesticide leaching assessment. Characterization of a wide range of pesticides as `leachers' or `non-leachers' for a specific Hawaii hydrogeological setting is facilitated by comparing the log-transformed AF, designated AFR, for each chemical with two reference chemicals for which leaching behavior in Hawaii is known. Defining a mean and uncertainty interval for the AFR index of each chemical being ranked provides a practical method of incorporating data uncertainty into a regulatory protocol.