Arsenic contamination of groundwater, soil and the consequent accumulation in rice has become recognised as a serious environmental problem in Bangladesh. Soil arsenic concentration has been found to vary across the landscape of Bangladesh. The overall management of the paddy soils play a critical role in the loading of arsenic into the soils, with the paddy soils having a higher content of arsenic than the adjacent non-irrigated soils, and soils irrigated with groundwater having a higher content of arsenic than those irrigated with surface water. While the surface waters in Bangladesh are at risk of toxic heavy metals contamination from a range of anthropogenic sources, inputs of toxic elements are expected in the paddy field soils irrigated by the contaminated surface waters posing a threat to the food security of Bangladesh. Moreover, land topological variations at the local level may make the mobilization and retention of arsenic and other geochemical elements more complex within the six inundation land types of Bangladesh.

Over 1200 surface paddy soil samples were collected from across Bangladesh, which were categorized according to inundation land type (highland, medium highland-1, medium highland-2, medium lowland, lowland, and very lowland) and by source of irrigation water (groundwater and surface water). While the groundwater irrigated paddy soils had significantly higher arsenic contents than in the surface water irrigated pddy soils, the contents of aluminium, cobalt, copper, iron, potassium, magnesium, molybdenum, nickel, lead, sodium, and zinc were significantly higher in the paddy soils irrigated with surface waters compared to the soils irrigated with groundwater. Highly significant variations (^ANOVAF = 24.74, p < 0.001) in the paddy soil arsenic contents were observed within the different inundation land types, following the order of very lowland > lowland > medium highland-2 > medium lowland > highland > medium highland-1, with the very lowland having the highest mean arsenic content of 9.95 mg/kg. Other geochemical elements analysed followed similar trends, with the exception of cadmium (the highest in the medium highland-2 (0.24 mg/kg), followed by highland (0.21 mg/kg)) in the paddy soils. Soil pH and the other geochemical elements analysed varied significantly (p < 0.001) across the inundation land types.

This study revealed that irrigating paddy soils with surface waters in Bangladesh increased toxic element loads in the soils. Elevated accumulation of the toxic elements in the low-lying flooded soils due to complex landscape topographical changes within the local areas poses a substantial risk to the rice cultivation, which is extensively done in those low level lands across Bangladesh. The present study thus gives high importance to further investigation of spatial and temporal variability and distribution of the geochemical elements in irrigated paddy fields with respect to the inundation land types in Bangladesh.