Interactions of Dimethylarsinic Acid, Total Arsenic and Zinc Affecting Rice Crop Management and Human Health in Cambodia

Disturbed nutrient accumulation and cell wall metabolism in panicles are responsible for rice straighthead disease

Rice straighthead disease substantially reduces crop yield, posing a significant threat to global food security. Dimethylarsinic acid (DMA) is the causal agent of straighthead disease and is highly toxic to the reproductive tissue of rice. However, the precise physiological mechanism underlying DMA toxicity remains unknown. In this study, six rice varieties with varying susceptibility to straighthead were utilized to investigate the growth performance and element distribution in rice panicles under DMA stress through pot experiments, as well as to explore the physiological response to DMA using transcriptomic methods. The findings demonstrate significant variations in both DMA accumulation and straighthead sensitivity among cultivars. The susceptible varieties exhibited higher DMA accumulation indices and displayed typical symptoms of straighthead disease, including erect panicles, deformed rachides and husks, and reduced seed setting rate and grain yield when compared to the resistant varieties. Moreover, DMA addition promoted mineral nutrients to accumulate in rachides and husks but less in grains. DMA showed preferential accumulation in rice grains with a distribution pattern similar to that of Copper (Cu) and zinc (Zn) within the panicle. Transcriptome analyses underscored the substantial impact of DMA on gene expression related to mineral metabolism. Notably, DMA addition significantly up-regulated the expression of pectin methylesterase, pectin lyase, polygalacturonase, and exogalacturonase genes in Nanjingxiangzhan, while these genes were down-regulated or weakly expressed in Ruanhuayou 1179. The alteration of pectin metabolic pathways induced by DMA may lead to abnormality of cell wall assembly and modification, thereby resulting in deformed rice panicles.

Uncertainty and sensitivity analyses of human health risk from bioaccessible arsenic exposure via rice ingestion in Bangkok, Thailand

BACKGROUND

Rice can be a source of arsenic (As) exposure, causing health impacts after ingestion.

OBJECTIVE

This study analyzed health risks due to As exposure through rice consumption, focusing on both bioaccessible (bAs) and total (tAs) As levels.

METHODS

Monte Carlo simulations were applied to determine health risk uncertainties and to analyze factors influencing health risks.

RESULTS

Cooked white and brown rice contained lower tAs and bAs than FAO/WHO standards of 0.20 and 0.35 mg/kg, respectively. As became less bioaccessible after cooking (14.0% in white rice and 18.5% in brown rice). Non-carcinogenic effects (MOS < 1) were found in 5% of children. Carcinogenic effects (MOE<100), especially lung cancer, were found in 75% of adults, with a probable incidence of 7 in 1,000,000. The lowest and highest annual cancer cases were 18 in 10,000,000 adolescents and 15 in 1,000,000 adults, respectively. The risks were mainly affected by body weight and bAs concentration.

SIGNIFICANCE

The results identified a certain risk level of non-carcinogenic effects in children and adolescents as well as carcinogenic effects in adults. The per capita consumption of rice in Thai adults should be reduced to prevent incidences of lung cancer.

The Role of Micronutrients and Toxic Metals in the Management of Epidemics in Cambodia

The illegal trade of wildlife in SE Asia has been identified as the likely cause of the COVID-19 pandemic. We reviewed 198 papers on the current COVID pandemic in Cambodia, diseases such as avian influenza and Nipah virus, most likely to develop into a new pandemic in Cambodia, and common features of disease that require mitigation. Artisanal goldmining uses pure mercury in the areas where wildlife is smuggled to China. Moreover, 30-40% of Cambodians are zinc deficient. High levels of arsenic in irrigation water (>1000 µg/L) are associated with very low levels of zinc in rice (5 µg/g) and rice is the primary staple food for the region. Brown rice from nine of 15 paddy fields in the arsenic zone of Cambodia had double the new guidelines of 100 µg/kg inorganic arsenic for children's food in the EU and USA. The combination of deficiencies of essential micronutrients like zinc and pervasive presence of arsenic and mercury has the potential to compromise the immunity of many Cambodians. Innovative solutions are suggested to improve micronutrient nutrition. Toxins that suppress the immune system must be better managed to reduce the virulence of pathogens. Cambodia was not likely the source of the COVID-19 but does have problems that could result in a new pandemic.