Potential Link between Spatial Variation and Translocation characteristics of Heavy Metals in Paddy topsoil and Human health risks in a CKDu prevalent area of Sri Lanka

M. R. D. L. Kulathunga, M. A. Ayanka Wijayawardena, Ravi Naidu and Sunil. J. Wimalawansa

Keywords:

Bio-accumulation, Chronic kidney disease, Heavy metal(loid)s, spatial variation, Transfer factor

Abstract:

The chronic kidney disease of unknown aetiology (CKDu) is confined to specific geographic areas of Sri Lanka. CKDu is a deadly disease that primarily affects farming communities, mainly male farmers. Due to the precise geolocation and geologically confined spread of this disease, continuing the CKDU research investigations, we investigated the geochemistry of the soil in connection with rice in affected areas. Previously, we showed the possibility that people living in CKDu endemic areas could be at risk of adverse health impacts from excessive Pb exposure, mainly through drinking food. Furthermore, if rice, the staple diet, carries high concentrations of Pb and other heavy metals and metalloids (such as As), these could also potentially bring about adverse health outcomes for people in the affected areas. Our current study aimed to characterise and map the spatial distribution of heavy metal(loid)s of V, Cr, Mn, Co, Cu, Zn, As, Se, Cd, and Pb in soil and rice samples. We also measured other essential soil properties, such as pH, electrical conductivity (EC), and organic matter (OM) in topsoil in Medirigiriya of the Polonnaruwa District in Sri Lanka, one of the CKDu affected areas. To better understand heavy metals exposure through the food chain, we calculated the bioaccumulation factors and transfer factors of the heavy metal(loid)s distribution among plant tissues. Covariance analysis showed an intrinsic heterogeneity of heavy metal distribution in the paddy soil. Spatial variation maps delineated the influence of irrigation and drainage water on the distribution of heavy metals in the study area. Results showed that rice plant roots were the primary tissues, which accumulated various heavy metal(loid)s. The distribution of heavy metal(loid)s in the rice plants’ edible portions (grains) was much less than in roots. We used the transfer factor (TF) to assess the concentration of metal(loid)s transported from soil to rice plants. The TF for the rice leaf to grain (TFL-G) was >1.0 for Cu and Pb in our study. We conclude that elevated Pb concentrations in paddy soils may be a factor in exposing people to harmful levels of this heavy metal over a prolonged period via the food chain, which can lead to chronic human health effects. While this study does not provide evidence that Pb causes CKDu, further research is indicated to assess the effects of excess intake of Pb and ill-health. However, our previously published research had indicated that the Pb content in rice grain exceeded WHO’s permissible limit for rice of 0.2 mg/kg. Since rice generated in these regions is transported throughout the country, health recommendations must be provided to everyone on how to process the rice for safe consumption. Based on the results, we propose implementing protective measures to reduce dietary Pb intake through rice and other means, to prevent adverse chronic health effects. We also recommend monitoring both the rice-growing topsoil and rice grains for contaminant metal accumulation, as a public health and harm prevention measure.