Quantitative and qualitative trapping of arsines deployed to assess loss of volatile arsenic from paddy soil

Arsenic volatilization in the environment is thought to be an important pathway for transfer from terrestrial pools to the atmosphere. However, this phenomenon is not well characterized due to inherent sampling issues in trapping, quantifying and qualifying these arsine gases; including arsine (AsH(3)), monomethyl arsine (MeAsH(2)), dimethyl arsine (Me(2)AsH) and trimethyl arsine (TMAs). To quantify and qualify arsines in air we developed a novel technique based on silver nitrate impregnated silica gel filled tubes. The method was characterized by measuring the recovery of trapped arsines after elution of this chemo-trap with hot boiling diluted nitric acid. Results from three separate experiments, measured by ICP-MS, showed that the method is reproducible and quantitative. Arsine species recovery ranged from 80.1 to 95.6%, with limit of detection as low as 3.8 ng per chemo-trap tube. Moreover, HPLC-ICP-MS analysis of hot boiling water eluted traps showed that the corresponding oxy ions of the arsines were formed with the As-C bonds of the molecule intact, hence, allowing qualification of trapped arsine species. A microcosm study examining volatile arsenic evolution from field contaminated Bangladeshi paddy soils (24.2 mg/kg arsenic) was used to show the application of silver nitrate chemo-trapping approach. Traps were placed on the inlet and the outlet of microcosms containing the soils that were either (cattle derived) manured or not, or flooded or not, in a factorial design. The headspace was purged with air at a flow rate of 12 mL/min. Results showed that as much as 320 ng of arsenic (0.014% of total soil content) could be emitted in a 3 week period for manured and flooded soils and that TMAs was the dominant species evolved, with lesser quantities of Me(2)AsH. No volatile arsenic evolution was observed for nonmanured treatments, and arsine release from the nonflooded, manured treatment was much less than the flooded treatment.

Baseline Soil Variation Is a Major Factor in Arsenic Accumulation in Bengal Delta Paddy Rice

Factors responsible for paddy soil arsenic accumulation in the tubewell irrigated systems of the Bengal Delta were investigated. Baseline (i.e., nonirrigated) and paddy soils were collected from 30 field systems across Bangladesh. For each field, soil sampled at dry season (Boro) harvest i.e., the crop cycle irrigated with tubewell water, was collected along a 90 m transect away from the tubewell irrigation source. Baseline soil arsenic levels ranged from 0.8 to 21. mg/kg, with lower values found on the Pliestocene Terrace around Gazipur (average, 1.6 +/- 0.2 mg/kg), and higher levels found in Holecene sediment tracts of Jessore and Faridpur (average, 6.6 +/- 1.0 mg/kg). Two independent approaches were used to assess the extent of arsenic build-up in irrigated paddy soils. First, arsenic build-up in paddy soil at the end of dry season production (irrigated - baseline soil arsenic) was regressed against number of years irrigated and tubewell arsenic concentration. Years of irrigation was not significant (P 0.711), indicating no year-on-year arsenic build-up, whereas tubewell As concentration was significant (P = 0.008). The second approach was analysis of irrigated soils for 20 fields over 2 successive years. For nine of the fields there was a significant (P <0.05) decrease in soil arsenic from year 1 to 2, one field had a significant increase, whereas there was no change for the remaining 10. Over the dry season irrigation cycle, soil arsenic built-up in soils at a rate dependent on irrigation tubewell water, 35* (tubewell water concentration in mg/kg, mg/L). Grain arsenic rises steeply at low soil/shoot arsenic levels, plateauing out at concentratations. Baseline soil arsenic at Faridpur sites corresponded to grain arsenic levels at the start of this saturation phase. Therefore, variation in baseline levels of soil arsenic leads to a large range in grain arsenic. Where sites have high baseline soil arsenic, further additional arsenic from irrigation water only leads to a gradual increase in grain arsenic concentration.

Occurrence and Partitioning of Cadmium, Arsenic and Lead in Mine Impacted Paddy Rice: Hunan, China

Paddy rice has been likened to nictiana sp in its ability to scavenge cadmium (Cd) from soil, whereas arsenic (As) accumulation is commonly an order of magnitude higher than in other cereal crops. In areas such as those found in parts of Hunan province in south central China, base-metal mining activities and rice farming coexist. Therefore there is a considerable likelihood that lead (Pb), in addition to Cd and As, will accumulate in rice grown in parts of this region above levels suitable for human consumption. To test this hypothesis, a widespread provincial survey of rice from mine spoilt paddies (n = 100), in addition to a follow-up market grain survey (n = 122) conducted in mine impacted areas was undertaken to determine the safety of local rice supply networks. Furthermore, a specific Cd, As, and Pb biogeochemical survey of paddy soil and rice was conducted within southern China, targeting sites impacted by mining of varying intensities to calibrate rice metal(loid) transfer models and transfer factors that can be used to predict tissue loading. Results revealed a number of highly significant correlations between shoot, husk, bran, and endosperm rice tissue fractions and that rice from mining areas was enriched in Cd, As, and Pb. Sixty-five, 50, and 34% of all the mine-impacted field rice was predicted to fail national food standards for Cd, As, and Pb, respectively. Although, not as elevated as the grains from the mine-impacted field survey, it was demonstrated that metal(loid) tainted rice was entering food supply chains intended for direct human consumption.

Behavior of simetryn and thiobencarb in the plough zone of rice fields

The behavior of simetryn and thiobencarb in flooded rice soil was investigated in a 2-year study. The concentrations of simetryn and thiobencarb were in the hundreds of μg kg^-1 in the top soil layer (0-5 cm) and became significantly lower in tens of μg kg^-1 in the deeper soil layers (5-10 and 10-15 cm). The half-lives of the two herbicides were also shorter (36 and 17 days for simetryn and thiobencarb, respectively) in the top soil layer, as they were most affected by environmental conditions, compared with corresponding values of 82 and 69 days in the 5-10 cm soil layer. Simetryn concentration was stable, while thiobencarb's half-life was 165 days in the 10-15 cm layer. About 35% of the applied mass of simetryn and thiobencarb were found in the rice soil compartment.

Analysis of parameter uncertainty and sensitivity in PCPF-1 modeling for predicting concentrations of rice herbicides

This paper demonstrates the procedures for probabilistic assessment of a pesticide fate and transport model, PCPF-1, to elucidate the modeling uncertainty using the Monte Carlo technique. Sensitivity analyses are performed to investigate the influence of herbicide characteristics and related soil properties on model outputs using four popular rice herbicides: mefenacet, pretilachlor, bensulfuron-methyl and imazosulfuron. Uncertainty quantification showed that the simulated concentrations in paddy water varied more than those of paddy soil. This tendency decreased as the simulation proceeded to a later period but remained important for herbicides having either high solubility or a high 1st-order dissolution rate. The sensitivity analysis indicated that PCPF-1 parameters requiring careful determination are primarily those involve with herbicide adsorption (the organic carbon content, the bulk density and the volumetric saturated water content), secondary parameters related with herbicide mass distribution between paddy water and soil (1st-order desorption and dissolution rates) and lastly, those involving herbicide degradations. © Pesticide Science Society of Japan.

Biotransfer of persistent organic pollutants from a large site in China used for the disassembly of electronic and electrical waste

Samples of groundwater, river water, river sediment, paddy soil, rice seeds, hen eggs, fish, umbilical cord blood, and newborn meconium were collected from October 2002 to October 2003 near a large site in China used for the disassembly of obsolete transformers and other electronic or electrical waste. Six indicator PCB congeners, three non-ortho dioxin-like PCB congeners, and six organochlorine pesticides were determined in the samples by GC with electron capture detector. The results demonstrated that the local environment and edible foods had been seriously polluted by toxic PCBs and organochlorine pesticides. The actual daily intakes (ADIs) of these pollutants were estimated for local residents living in the area. The intake data showed that the contents of PCBs in these local residents were substantial, as the ADI estimates greatly exceed the reference doses set by the World Health Organization and the United States Agency for Toxic Substances and Disease Registry. The presence of the indicator PCB congeners in the cord blood and the meconium samples, as well as significant correlations (r(2) > 0.80, p < 0.05) between these levels, suggests a potential biotransfer of these indicators from mothers to their newborns. This preliminary study showed that obsolete transformers and other electronic or electrical waste can be an important source for the emission of persistent organic pollutants into the local environment, such as through leakage, evaporation, runoff, and leaching. Contamination from this source appears to have reached the level considered to be a serious threat to environmental and human health around the disassembly site.

稗草对水稻及稻田土壤微生物的干扰作用

稗草对水稻的干扰一直是水稻生产中的难题，这种干扰不仅包括竞争和化感作用，而且还有土壤理化因子、土壤微生物和一些土壤酶的参与，所以本研究从水稻、稗草和土壤因子三者相互作用的角度探讨稗草对水稻的干扰作用，主要结论如下： 1、田间条件下，水稻和稗草共生土壤的各种养分在水稻根系附近的分布更丰富，稗草对养分的消耗能力强于水稻；共生处理，化感水稻品种PI312777根区养分含量明显升高，而普通水稻品种辽粳9根区土壤养分含量降低。 2、和稗草共生，PI312777和辽粳9根区土壤中微生物生物量C含量均显著下降，稗草受水稻的影响微生物生物量C含量也被抑制。化感水稻PI312777根系周围细菌和自生固氮菌数量显著增加，真菌、氨化细菌的数量明显下降，而放线菌无明显变化；普通水稻根系周围细菌、真菌、放线菌及氨化细菌数量均显著减少，自生固氮菌数量明显增加。 3、从脱氢酶、脲酶、转化酶和多酚氧化酶活性的变化比较两个水稻品种对抗稗草干扰的能力，化感品种PI312777的表现明显优于普通水稻辽粳9，稗草的存在显著诱导促进了PI312777根区土壤脲酶、转化酶和多酚氧化酶的活性。 4、稗草群体的生命活动对土壤主要微生物类群包括细菌、放线菌、自生固氮菌及氨化细菌的生长和繁殖均有促进作用，而对真菌数量表现为显著抑制。适当的稗草群体对土壤养分的活化作用明显，包括土壤中总N、总P和总K，提高了铵态氮、有效P及速效K的含量，而稗草密度过大则会过量消耗土壤养分。稗草群体的生命活动促进了土壤中脱氢酶、脲酶、转化酶和多酚氧化酶的活性。 5、稗草萌发液及稗草的伴生对三叶期化感水稻化感物质有诱导作用，而且稗草萌发液对水稻的萌发和生长均有抑制作用，尤其对普通水稻品种辽粳9，表明稗草萌发液对水稻有抑制作用。 6、稗草萌发液促进土壤细菌和放线菌的数量，随培养时间的延长，高浓度稗草萌发液的促进作用更明显；真菌和自生固氮菌被高浓度稗草萌发液抑制，而自生固氮菌在培养时间7天以后，适当的浓度可以促进其繁殖。

水稻化感物质对土壤微生物的作用

本文主要目的是探讨水稻化感品种对土壤微生物的影响，为进一步阐明水稻化感品种与稻田微生物的生物化学关系奠定基础。在分离出两种水稻化感物质黄酮甙基础上，首先研究水稻化感物质对环境因子的响应情况。同时，探讨土壤中黄酮甙的降解动态和水稻组织及其释放到培养基质中的黄酮甙浓度情况，并用土壤薄层层析和生测实验研究黄酮甙在土壤中的迁移性。随后系统研究水稻化感品种幼苗、萌发液、根分泌物以及水稻化感物质黄酮甙对土壤微生物的作用。结果表明： 1、虽然化感物质释放程度和环境因子有关，但主要取决于水稻自身的化感特性。黄酮甙进入土壤10 h后消失，生成稳定的黄酮甙元，这种甙元是水稻真正的化感物质，因此，黄酮甙是水稻化感品种存储化感物质的形式，而不是真正起作用的物质。 2、水稻化感品种根际土壤中的微生物数量受到显著的抑制作用，根际土壤微生物的群落结构和对照土壤相似，和水稻非化感品种根际土壤微生物的群落结构不同。 3、向土壤中施加萌发液和根系分泌物初期，土壤细菌、氨化细菌、放线菌数量表现为水稻非化感品种大于水稻化感品种。水稻化感品种土壤中的微生物生物量碳受到抑制，而真菌生物量受到促进。萌发液土壤中对照和水稻化感品种群落结构变化相似，根分泌物土壤中对照和水稻非化感品种群落结构变化相似。 4、施加低浓度黄酮甙土壤中的细菌、氨化细菌以及真菌数量均高于高浓度黄酮甙土壤中的数量，但是土壤中的放线菌和真菌生物量却表现为：随着土壤中黄酮甙浓度升高，受到的抑制作用增强。在添加浓度范围内，黄酮甙对土壤微生物群落结构产生不同影响。

稻田化感物质对土壤微生物和酶的作用及其迁移行为

本论文以化感水稻品种PI312777和非化感水稻品种辽粳9为试验材料，研究田间全生育时期内两种水稻根际土壤微生物及酶活性的变化；室内添加两种水稻苗期根系分泌物、水稻及稗草化感物质，探讨其对土壤微生物及酶活性的影响。测定指标有：土壤微生物生物量碳、微生物数量(细菌、放线菌、真菌、氨化细菌和好气性自生固氮菌)、土壤酶(脲酶、转化酶、脱氢酶和多酚氧化酶)活性和磷酸脂肪酸谱图分析。同时利用土壤薄层层析结合生物测定的方法研究化感物质在不同类型土壤中的迁移性能，结果表明： 1.种植水稻明显提高了土壤微生物生物量碳、微生物数量和酶活性。在生长的初始阶段(苗期到分蘖期)，化感水稻PI312777根际土壤微生物各项指标及酶活性均高于非化感水稻辽粳9。 2.两种水稻苗期根系分泌物均刺激土壤微生物并间接提高土壤酶活性，改变土壤微生物群落组成，处理间的效应因培养时间和水分条件而不同。 3.稗草化感物质——对羟基扁桃酸对水稻生长及土壤微生物的影响因浓度而呈现不同的效应。水稻化感物质对土壤微生物有不同的影响。苯甲酸和阿魏酸刺激土壤微生物及酶活性；黄酮对土壤微生物生物量碳和真菌数量有抑制作用。水分条件的变化导致微生物群落结构的改变，淹水条件下环丙基脂肪酸(cy17:0和cy19:0)及真菌脂肪酸含量减少。 4.不同化感物质在同一土壤中的迁移性能不同，而同一化感物质在不同土壤中的移动性也有差异；比移值Rf与土壤有机质含量、粘粒含量、阳离子交换量呈负相关，与土壤pH呈正相关。