Lead in rice: analysis of baseline lead levels in market and field collected rice grains

In a large scale survey of rice grains from markets (13 countries) and fields (6 countries), a total of 1578 rice grain samples were analysed for lead. From the market collected samples, only 0.6% of the samples exceeded the Chinese and EU limit of 0.2 μg g(-1) lead in rice (when excluding samples collected from known contaminated/mine impacted regions). When evaluating the rice grain samples against the Food and Drug Administration's (FDA) provisional total tolerable intake (PTTI) values for children and pregnant women, it was found that only people consuming large quantities of rice were at risk of exceeding the PTTI from rice alone. Furthermore, 6 field experiments were conducted to evaluate the proportion of the variation in lead concentration in rice grains due to genetics. A total of 4 of the 6 field experiments had significant differences between genotypes, but when the genotypes common across all six field sites were assessed, only 4% of the variation was explained by genotype, with 9.5% and 11% of the variation explained by the environment and genotype by environment interaction respectively. Further work is needed to identify the sources of lead contamination in rice, with detailed information obtained on the locations and environments where the rice is sampled, so that specific risk assessments can be performed.

Variation in rice cadmium related to human exposure

Cereal grains are the dominant source of cadmium in the human diet, with rice being to the fore. Here we explore the effect of geographic, genetic, and processing (milling) factors on rice grain cadmium and rice consumption rates that lead to dietary variance in cadmium intake. From a survey of 12 countries on four continents, cadmium levels in rice grain were the highest in Bangladesh and Sri Lanka, with both these countries also having high per capita rice intakes. For Bangladesh and Sri Lanka, there was high weekly intake of cadmium from rice, leading to intakes deemed unsafe by international and national regulators. While genetic variance, and to a lesser extent milling, provide strategies for reducing cadmium in rice, caution has to be used, as there is environmental regulation as well as genetic regulation of cadmium accumulation within rice grains. For countries that import rice, grain cadmium can be controlled by where that rice is sourced, but for countries with subsistence rice economies that have high levels of cadmium in rice grain, agronomic and breeding strategies are required to lower grain cadmium.

Organic matter-solid phase interactions are critical for predicting arsenic release and plant uptake in Bangladesh paddy soils

Agroecological zones within Bangladesh with low levels of arsenic in groundwater and soils produce rice that is high in arsenic with respect to other producing regions of the globe. Little is known about arsenic cycling in these soils and the labile fractions relevant for plant uptake when flooded. Soil porewater dynamics of field soils (n = 39) were recreated under standardized laboratory conditions to investigate the mobility and interplay of arsenic, Fe, Si, C, and other elements, in relation to rice grain element composition, using the dynamic sampling technique diffusive gradients in thin films (DGT). Based on a simple model using only labile DGT measured arsenic and dissolved organic carbon (DOC), concentrations of arsenic in Aman (Monsoon season) rice grain were predicted reliably. DOC was the strongest determinant of arsenic solid-solution phase partitioning, while arsenic release to the soil porewater was shown to be decoupled from that of Fe. This study demonstrates the dual importance of organic matter (OM), in terms of enhancing arsenic release from soils, while reducing bioavailability by sequestering arsenic in solution.

Mitigation of arsenic contamination in irrigated paddy soils in South and South-East Asia

It has recently become apparent that arsenic-contaminated groundwater used for irrigation in several countries of South and South-east Asia is adding arsenic to soils and rice, thus posing a serious threat to sustainable agricultural production and to the health and livelihoods of affected people in those countries. This paper describes the many environmental, agricultural and social factors that determine practical mitigation strategies and research needs, and describes possible mitigation measures that need to be tested. These measures include providing alternative irrigation sources, various agronomic measures, use of soil amendments, growing hyperaccumulator plants, removing contaminated soil and using alternative cooking methods.

Arsenic in groundwater: a threat to sustainable agriculture in South and South-east Asia

The problem of arsenic pollution of groundwater used for domestic water supplies is now well recognised in Bangladesh, India and some other countries of South and South-east Asia. However, it has recently become apparent that arsenic-polluted water used for irrigation is adding sufficient arsenic to soils and rice to pose serious threats to sustainable agricultural production in those countries and to the health and livelihoods of affected people. This paper reviews the nature of those threats, taking into account the natural sources of arsenic pollution, areas affected, factors influencing arsenic uptake by soils and plants, toxicity levels and the dietary risk to people consuming arsenic-contaminated rice.

Structural and functional definition of the human chitinase chitin-binding domain

Mammalian chitinase, a chitinolytic enzyme expressed by macrophages, has been detected in atherosclerotic plaques and is elevated in blood and tissues of guinea pigs infected with Aspergillus. Its normal physiological function is unknown. To understand how the enzyme interacts with its substrate, we have characterized the chitin-binding domain. The C-terminal 49 amino acids make up the minimal sequence required for chitin binding activity. The absence of this domain does not affect the ability of the enzyme to hydrolyze the soluble substrate, triacetylchitotriose, but abolishes hydrolysis of insoluble chitin. Within the minimal chitin-binding domain are six cysteines; mutation of any one of these to serine results in complete loss of chitin binding activity. Analysis of purified recombinant chitin-binding domain revealed the presence of three disulfide linkages. The recombinant domain binds specifically to chitin but does not bind chitosan, cellulose, xylan, beta-1, 3-glucan, beta-1,3-1,4-glucan, or mannan. Fluorescently tagged chitin-binding domain was used to demonstrate chitin-specific binding to Saccharomyces cerevisiae, Candida albicans, Mucor rouxii, and Neurospora crassa. These experiments define structural features of the minimal domain of human chitinase required for both specifically binding to and hydrolyzing insoluble chitin and demonstrate relevant binding within the context of the fungal cell wall.

Profile of human macrophage transcripts: insights into macrophage biology and identification of novel chemokines

High throughput partial sequencing of randomly selected cDNA clones has proven to be a powerful tool for examining the relative abundance of mRNAs and for the identification of novel gene products. Because of the important role played by macrophages in immune and inflammatory responses, we sequenced over 3000 randomly selected cDNA clones from a human macrophage library. These sequences represent a molecular inventory of mRNAs from macrophages and provide a catalog of highly expressed transcripts. Two of the most abundant clones encode recently identified CC chemokines. Macrophage-derived chemokine (MDC) plays a complex role in immunoregulation and is a potent chemoattractant for dendritic cells, T cells, and natural killer cells. The chemokine receptor CCR4 binds MDC with high affinity and also responds by calcium flux and chemotaxis. CCR4 has been shown to be expressed by Th2 type T cells. Recent studies also implicate MDC as a major component of the host defense against human immunodeficiency virus.