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A comparative study of arsenic enrichment in the Bengal Delta (BD) was carried out in three alluvial aquifers in south-central Bangladesh. Investigated sites included Sonargaon in Narayanganj, Chandina in Comilla and Sirajdikhan in Munshiganj districts. At all sites samples from different depths were collected, and water chemistry and redox status vs. depth trends were determined. The concentrations of DOC and HCO3 − were highest at Sirajdikhan site, while at the Sonargaon and Chandina sites the concentrations were lower. On the contrary, the NH4 + concentration was high at the Chandina site as compared to the other sites. There was a good match between dissolved As and Fe at the Sirajdikhan and Sonargaon sites, but not at the Chandina site. The dissolved aqueous concentration of Mn was low at the Chandina site, which suggested that the Mn(IV) redox buffering step was missing. Speciation modeling indicated a possibility of siderite precipitation at all sites, but precipitation of rhodochrosite only at the Sonargaon and Sirajdikhan sites. At the Sirajdikhan site, the log $$ {\text{P}}_{{{\text{CO}}_{ 2} }} $$ values were very high (−1.37), which revealed the production of CO2 in redox processes. Principal component analysis (PCA) indicated an impact of sea water and redox status of different samples. These results suggest that the dissolved As is de-coupled from dissolved Mn because when released, As is re-adsorbed onto the Fe(III) minerals in solid phase, as well as from dissolved Fe when precipitation of Fe(II) minerals controls the aqueous concentrations of Fe. In addition, several other concurrent redox processes may exert kinetic constraints depending on refractory characteristics of Fe(III) minerals.

1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (p,p′-DDT) is a recalcitrant organic compound that is difficult to remove from contaminated soil due to its low solubility. In this study we investigated the effectiveness of both cosolvents and surfactants in enhancing the solubility of p,p′-DDT from a soil that has been contaminated with DDT for nearly 40 yr. The presence of selected surfactants removed less than 1 to 11% of p,p′-DDT compared to cosolvents, which removed less than 1 to 77% of p,p′-DDT from the same soil. The low solubility of p,p′-DDT in the presence of surfactants was attributed to the decreased surfactant concentration to below critical micelle concentrationfollowing sorption by soil surfaces. Enhanced solubility of p,p′-DDT was achieved with the use of cosolvents that releasedup to 77% of p,p′-DDT from a contaminated soil. Increasing the solution concentration and hydrophobicity of the cosolvent increased the amount of p,p′-DDT desorbed. For example, the amount of p,p′-DDT desorbed increased in the order 5% 1-propanol << 50% ethanol << 50% 1-propanol. Repeated washing of the soil with various cosolvents, in all but two cases, markedly increased the total amount of p,p′-DDT desorbed from the soil. For example, repeated washing of the soil with 50% ethanol increased the amount of p,p′-DDT removed by 42% while repeated washings of the soil with 50% 1-propanol had little effect on the amount of p,p′-DDT desorbed. Increasing the soil-solution ratio from 1:2 to 1:10 in the presence of 40% 1-propanol increased the amount of p,p′-DDT desorbed by 100%; suggesting that the soil-solution ratio was an important parameterin controlling the amount of p,p′-DDT desorbed.