Fractionation of Added Cadmium in Submerged Soils asAffected by Organic Materials

The effect of three organic materials (rice straw, Chinese milk vetch and pig manure) on the fractionationof cadmium added into two soils (a red soil and a fiuvo-aquic soil) was studied using submerged incubationexperiment. The organic materials increased soil solid organic carbon (SOC), pH value, the concentration ofactive Si in all the treatments and active Fe and Mn in some treatments. Accumulated SOC caused directlythe increase of Cd bound to solid organic matter and consequently the decrease of exchangeable Cd. Higheractive Si and pH, as well as lower Eh, were also responsible for the reduction of exchangeable Cd. Cd boundto Mn oxide was positively correlated with pH values and rose significatly after one-month incubation, butdecreased after three-month incubstion. Cd bound to amorphous Fe oxide increased with the incubationtime, but was not effected significantly by adding organic materials.

Alteration of certain soil microbiological and biochemical indices of a paddy soil under anthropogenic stress

A 21-day laboratory incubation experiment was conducted to investigate the impact of pesticides (insecticide, herbicide, fungicide) on paddy field soil health under controlled moisture (flooded soil) and temperature (25 ℃) environment. The electron transport system (ETS)/Dehydrogenase activity showed negative correlation with pesticides concentrations, decreased with increase of pesticide concentration. The higher doses(5 to 10 times field rates) of pesticides significantly inhibited ETS activity, while lower rates failed to produce any significant reducing effect on the control. The toxicity of pesticides in decreasing the ETS activity was in the order: insecticide > fungicide > herbicide, irrespective of their rates of application. The pesticides increased the soil phenol content, which increased with increasing concentration of agrochemicals. The pesticide application did not produce any significant change in soil protein content. The response of biomass phospholipid content was nearly similar to that of ETS activity. The phospholipid content decreased with the addition of pesticides in the order insecticide > fungicide > herbicide and the toxicity was in the order: 10 FR (field rate) > 5 FR > 1.0 FR > 0.5 FR > control.

Persistence of Dioxin TCDD in Southern Vietnam Soil and Water Environments and Maternal Exposure Pathways with Potential Consequences on Congenital Heart Disease Prevalence in Vietnam

Waterlogged soils and submerged sediments in wetlands and agricultural lands used for rice paddies and aquaculture have anaerobic conditions that slow and prevent the photo and microbial degradation of dioxin TCDD (2,3,7,8-tetracholorodibenzo-p-dioxin), enabling it to persist in environments for long periods. Over 1.6 million ha of land in southern Vietnam were sprayed with 2,4,5-T herbicides (e.g. Agent Orange) contaminated with dioxin TCDD during the Vietnam War (1961-1971);45% of these ha received four or more spray flight missions. Dioxins are endocrine disrupters and may induce cardiovascular disease, growth, and developmental defects, diabetes, hormonal dysfunctions and disruptions, certain cancers, and chloracne. Outpatient screening clinic 2020 data on Vietnamese children suspected of congenital heart disease (CHD) showed the childhood CHD prevalence rate in Vietnam of 13.356/1000, significantly elevated compared to the Asian CHD prevalence rate of 3.531/1000. CHD prevalence rate differences between North Vietnam (2.541/1000) and south of the 17th parallel (10.809/1000) were significant. Vietnamese farmers, especially pregnant women whose occupations involve daily contact with soil and sediments where dioxin TCDD persists in the environment may be at risk of dioxin accumulation from dermal exposure and bioaccumulation via diet. There is an urgent need for funded longitudinal genetic and clinical studies to assess CHD and other organ system childhood malformations due to in utero TCDD exposure. We recommend an integrated research design involving 1) site-specific locations that received high volumes and multiple spray loads of herbicides during the Vietnam War;2) soil sampling of submerged and waterlogged soils and sediments where TCDD may not have degraded;3) production areas of agriculture, fisheries, and other aquatic products;4) risk assessment dioxin levels in foods where TCDD is likely to bioaccumulate;5) child-bearing age and pregnant women with potentially high sensitivity to long-term low dose exposure, and 6) men and women in occupations that are in daily contact with contaminated soil and sediments as part of their job routines.

Iron Toxicity Tolerance of Rice Genotypes in Relation to Growth,Yield and Physiochemical Characters

Iron(Fe)toxicity,generated from excess reduced ferrous Fe(Fe^(2+))ion formation within the soil under submerged condition,is a potent environmental stress that limits lowland rice production.Total 11 diverse Thai rice genotypes,including a recognized tolerant genotype Azucena and a susceptible genotype IR64,were evaluated against 5 Fe^(2+)levels[0(control),150,300,600 and 900 mg/L]to screen the tested genotypes for their Fe-toxicity tolerance and to classify them as a sensitive/tolerant category.The evaluation was conducted by a germination study,followed by a polyhouse study on growth,yield and physiochemical performances.Results showed significant variations in Fe^(2+)-tolerance across genotypes.Increasing Fe^(2+)level beyond 300 mg/L was detrimental for germination and growth of all the tested genotypes,although germination responses were negatively affected at Fe^(2+)≥300 mg/L.Physiochemical responses in the form of leaf greenness,net photosynthetic rate,membrane stability index and Fe contents in leaf and root were the most representative of Fe^(2+)-toxicity-mediated impairments on overall growth and yield.Difference in physiochemical responses was effectively correlated with the contrasting ability of the genotypes on lowering excess Fe^(2+)in tissues.Analysis of average tolerance and stress tolerance index unveiled that the genotypes RD85 and RD31 were the closest to the tolerant check Azucena and the sensitive check IR64,respectively.The unweighted pair group method with arithmetic means clustering revealed three major clusters,with cluster Ⅱ(four genotypes)being Fe^(2+)tolerant and cluster Ⅰ(four genotypes)being Fe^(2+)sensitive.Principal component(PC)analysis and genotype by trait-biplot analysis showed that the first two components explained 90.5%of the total variation,with PC1 accounting for 56.6%and PC2 for 33.9%of the total variation.The identified tolerant rice genotypes show potentials for cultivation in Fe^(2+)-toxic lowlands for increased productivity.The findings contribute to the present understanding on Fe^(2+)-toxicity response and provide a basis for future genotype selection or rice crop improvement programs against Fe^(2+)-toxicity.