Chronic renal failure among farm families in cascade irrigation systems in Sri Lanka associated with elevated dietary cadmium levels in rice and freshwater fish (Tilapia)

Chronic renal failure (CRF), in the main agricultural region under reservoir based cascade irrigation in Sri Lanka has reached crisis proportion. Over 5,000 patients in the region are under treatment for CRF. The objective of this study is to establish the etiology of the CRF. Concentrations of nine heavy metals were determined in sediments, soils of reservoir peripheries, water and Nelumbo nucifera (lotus) grown in five major reservoirs that supply irrigation water. All five reservoirs carried higher levels of dissolved cadmium (Cd), iron (Fe) and lead (Pb). Dissolved Cd in reservoir water ranged from 0.03 to 0.06 mg/l. Sediment Cd concentration was 1.78-2.45 mg/kg. No arsenic (As) was detected. Cd content in lotus rhizomes was 253.82 mg/kg. The Provisional Tolerable Weekly Intake (PTWI) of Cd based on extreme exposure of rice is 8.702-15.927 mug/kg body weight (BW) for different age groups, 5-50 years. The PTWI of Cd due to extreme exposure of fish is 6.773-12.469 mug/kg BW. The PTWI on a rice staple with fish is 15.475-28.396 mug/kg BW. The mean urinary cadmium (UCd) concentration in CRF patients of age group 40-60 years was 7.58 mug Cd/g creatinine and in asymptomatic persons UCd was 11.62 mug Cd/g creatinine, indicating a chronic exposure to Cd. The possible source of Cd in reservoir sediments and water is Cd-contaminated agrochemicals. The CRF prevalent in north central Sri Lanka is a result of chronic dietary intake of Cd, supported by high natural levels of fluoride in drinking water, coupled with neglecting of routine de-silting of reservoirs for the past 20 years.     

Effect of chemical amendments on remediation of potentially toxic trace elements (PTEs) and soil quality improvement in paddy fields

Remediation of potentially toxic trace elements (PTEs) in paddy fields is fundamental for crop safety. In situ application of chemical amendments has been widely adapted because of its cost-effectiveness and environmental safety. The main purpose of this research was to (1) evaluate the reduction in dissolved concentrations of cadmium (Cd) and arsenic (As) with the application of chemical amendments and (2) monitor microbial activity in the soil to determine the remediation efficiency. Three different chemical amendments, lime stone, steel slag, and acid mine drainage sludge, were applied to paddy fields, and rice (Oryza sativa L. Milyang 23) was cultivated. The application of chemical amendments immobilized both Cd and As in soil. Between the two PTEs, As reduction was significant (p < 0.05) with the addition of chemical amendments, whereas no significant reduction was observed for Cd than that for the control. Among six soil-related variables, PTE concentration showed a negative correlation with soil pH (r = ?0.70 for As and r = ?0.54 for Cd) and soil respiration (SR) (r = ?0.88 for As and r = ?0.45 for Cd). This result indicated that immobilization of PTEs in soil is dependent on soil pH and reduces PTE toxicity. Overall, the application of chemical amendments could be utilized for decreasing PTE (As and Cd) bioavailability and increasing microbial activity in the soil.     

珠江三角洲稻田土壤砷及其向水稻籽粒迁移特征

采集珠江三角洲区域水稻(Oryze sativa L.)植株的根系、秸秆、稻谷和对应的耕层土壤(0～15锄)样品,分析土壤和水稻植株中砷含量,初步研究土壤砷与土壤基本理化性质的关系及砷在土壤-水稻系统中的迁移规律.结果表明,土壤砷含量在1.83～18.14 mg·kg~(-1)之间,土壤砷与土壤有机质、砂粒含量呈显著负相关,与土壤粉粒含量呈显著正相关.糙米中的砷含量在0.21～0.43mg·kg~(-1)之间,均未超过国家食品卫生标准(0.7mg·kg~(-1)),砷在水稻植株中的分布规律为根>秸秆>颖壳>糙米.糙米砷含量与秸秆砷含量呈极显著正相关,与秸秆中P/As、Si/As摩尔比呈极显著负相关,因此,降低秸秆中As的积累、增加秸秆中P、Si的积累可降低水稻籽粒中的砷含量.