Field fluxes and speciation of arsines emanating from soils

The biogeochemical cycle of arsenic (As) has been extensively studied over the past decades because As is an environmentally ubiquitous, nonthreshold carcinogen, which is often elevated in drinking water and food. It has been known for over a century that micro-organisms can volatilize inorganic As salts to arsines (arsine AsH(3), mono-, di-, and trimethylarsines, MeAsH(2), Me(2)AsH, and TMAs, respectively), but this part of the As cycle, with the exception of geothermal environs, has been almost entirely neglected because of a lack of suited field measurement approaches. Here, a validated, robust, and low-level field-deployable method employing arsine chemotrapping was used to quantify and qualify arsines emanating from soil surfaces in the field. Up to 240 mg/ha/y arsines was released from low-level polluted paddy soils (11.3 ± 0.9 mg/kg As), primarily as TMAs, whereas arsine flux below method detection limit was measured from a highly contaminated mine spoil (1359 ± 212 mg/kg As), indicating that soil chemistry is vital in understanding this phenomenon. In microcosm studies, we could show that under reducing conditions, induced by organic matter (OM) amendment, a range of soils varied in their properties, from natural upland peats to highly impacted mine-spoils, could all volatilize arsines. Volatilization rates from 0.5 to 70 µg/kg/y were measured, and AsH(3), MeAsH(2), Me(2)AsH, and TMAs were all identified. Addition of methylated oxidated pentavalent As, namely monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA), to soil resulted in elevated yearly rates of volatilization with up to 3.5% of the total As volatilized, suggesting that the initial conversion of inorganic As to MMAA limits the rate of arsine and methylarsines production by soils. The nature of OM amendment altered volatilization quantitatively and qualitatively, and total arsines release from soil showed correlation between the quantity of As and the concentration of dissolved organic carbon (DOC) in the soil porewater. The global flux of arsines emanating from soils was estimated and placed in the context of As atmospheric inputs, with arsines contributing from 0.9 to 2.6% of the global budget.

Antimony bioavailability in mine soils

Five British former mining and smelting sites were investigated and found to have levels of total Sb of up to 700 mg kg(-1), indicating high levels of contamination which could be potentially harmful. However, this level of Sb was found to be biologically unavailable over a wide range of pH values, indicating that Sb is relatively unreactive and immobile in the surface layers of the soil, remaining where it is deposited rather than leaching into lower horizons and contaminating ground water. Sb, sparingly soluble in water, was unavailable to the bacterial biosensors tested. The bioluminescence responses were correlated to levels of co-contaminants such as arsenic and copper, rather than to Sb concentrations. This suggests that soil contamination by Sb due to mining and smelting operations is not a severe risk to the environment or human health provided that it is present as immobile species and contaminated sites are not used for purposes which increase the threat of exposure to identified receptors. Co-contaminants such as arsenic and copper are more bioavailable and may therefore be seen as a more significant risk.

A review of the global pesticide legislation and the scale of challenge in reaching the global harmonization of food safety standards

Pesticide use is important in agriculture to protect crops and improve productivity. However, they have the potential to cause adverse human health or environmental effects, dependent on exposure levels. This review examines existing pesticide legislation worldwide, focusing on the level of harmonisation, and impacts of differing legislation on food safety and trade. Pesticide legislation varies greatly worldwide as countries have different requirements guidelines and legal limits for plant protection. Developed nations have more stringent regulations than developing countries, which lack the resources and expertise to adequately implement and enforce legislation. Global differences in pesticide legislation act as a technical barrier to trade. International parties such as the European Union (EU), Codex Alimentarius Commission (Codex), and North American Free Trade Agreement (NAFTA) have attempted to harmonise pesticide legislation by providing maximum residue limits (MRLs), but globally these limits remain variable. Globally harmonised pesticide standards would serve to increase productivity, profits and trade, and enhance the ability to protect public health and the environment. 

Influence of phosphate addition on the arsenic uptake by wheat (Triticum Durum) grown in arsenic polluted soils

Arsenic (As) uptake and distribution in the roots, shoots, and grain of wheat (Triticum durum) grown in 2 As polluted soils (192 and 304 mg kg ^-1 respectively), and an uncontaminated soil (14 mg kg^-1 ), collected from Scarlino plain (Tuscany, Italy), was investigated with respect with phosphorus fertilization. Three different level of phosphorus (P) fertilization: PO [0 kg ha^-1], Pl [75 kg ha^-1], and P2 [150 kg ha^-1], as KH₂PO₄ of P, were applied. The presence of high concentrations of As in soils reduced plants growth, decreased grain yield and increased root, shoot and grain As concentrations, especially in the absence of P fertilization. The P fertilization decreased the As concentration in all the tissues as well as the translocation of As to the shoot and grain. This observation may be useful in certain areas of the world with high levels of As in soils, to reduce the potential risk posed to human health by As entering the food-chain. © by PSP.

Physico-geochemical and mineral composition of neem tree soils and relation to organic properties

The Neem tree, the oil of which has a long history of pesticide, fertilizer and medicinal use in India, has been studied extensively for its organic compounds. Here we present a physical, mineralogical and geochemical database resulting from the analyses of two Neem soil profiles (epipedons) in India. Neem tree derivatives are used in the manufacture of a variety of products, from anti-bacterial drugs and insecticides to fertilizers and animal feeds. A preliminary geochemical and mineralogical analysis of Neem soils is made to explore the potential for chemical links between Neem tree derivatives and soils. Physical soil characteristics, including colour, texture and clay mineralogy, suggest the two pedons formed under different hydrological regimes, and hence, are products of different leaching environments, one well-drained site, the other poorly drained. Geochemically, the two Neem soils exhibit similarities, with elevated concentrations of Th and rare earth elements. These elements are of interest because of their association with phosphates, especially monazite and apatite, and the potential link to fertilizer derivatives. Higher concentrations of trace elements in the soils may be linked to nutritional derivatives and to cell growth in the Neem tree.