Mobilisation of arsenic in sedimentary aquifers may be, in part, a result of changes in the geohydrochemical environment due to agricultural irrigation. In the deeper subsurface, elevated arsenic concentration is associated with compaction caused by groundwater withdrawal. Experts say that an understanding of geochemical principles is essential for an explanation of the mobilisation of arsenic by natural processes. Along with supergenic mobilisation of elements arsenic is transferred from one phase to another or within a heterogeneous phase such as soil by microbial mediated processes. Aerobic bacteria and fungi often transform arsenic into coordination complexes that are more mobile in soil water than the uncomplexed cation.
Movement is a strong function of speciation and soil type.
Soil pH also influences arsenic mobility. Although there are two layers south of West Bengal and in Bangladesh, these 2 layers combined together to form a thick layer in the northwestern part, especially in the Malda district of West Bengal. As the aquifers are hydraulically connected, people should get some arsenic. It depends on the thickness of the layer and aquifers. In the north-western part of Bangladesh, the rainfall is less than the groundwater recharge.