:: Journal of International Environmental Application & Science ::

Year 2008, Volume III (Issue I)

Journal of International Environmental Application and Science , Vol. 3, No. 1 (2008), 1-20

Influence of several factors during collection and preservation prior to analysis of arsenic in groundwater: A case study from West Bengal, India

Tarit Roychowdhury 1

1School of Environmental Studies, Jadavpur University, Kolkata 700032, West Bengal, India
2Geo-Environment Management Division, National Environmental Engineering Research Institute, Nehru Marg, Nagpur 440020, Maharasthra, India

Abstract: To avoid the discrepancy in analytical results, sets of experiments were studied on mode of sampling, sample storage and time interval study and its effect were noted on groundwater arsenic concentration from West Bengal, India. Arsenic concentration decreased gradually with time and higher iron concentration, higher arsenic loss (due to co-precipitation with iron) was observed for non-acidified samples. Somewhat lesser loss of arsenic was observed under refrigerated condition, compared to room temperature and about 99% of iron was lost within a day under non-acidified condition. About 91-98% and 96-100% of arsenic were recovered within first three days for acidified samples, stored in room temperature and refrigerated condition, respectively. A considerable amount of arsenic was lost with time due to the adsorption on plastic container surface/precipitation with other elements/volatilization, especially for acidified water samples. Linear regressions showed very good correlations between initial iron concentration and loss of arsenic for non-acidified samples. Particulates (colloidal iron hydroxide) present in pumped groundwater contributed a considerable amount of arsenic and with time, less to lesser particles was coming out with pour water. Average 166% and 23.5% (up to five and fifteen months from installation, respectively) higher results of arsenic were observed for the unfiltered waters compared to the filtered (Millipore membrane filter, 0.45 µm), collected from the newly installed tubewells, 1 month and 11 months old, respectively. Whereas, an average 12% higher value of arsenic was observed in unfiltered waters compared to the filtered, for the older tubewells, 2-9 years old. Very good correlations were observed between water arsenic concentrations in filtered and unfiltered samples for older tubewells. An average ±14% variation of both arsenic and iron concentrations in groundwater (n=23) was observed round the year.  
Keywords: Groundwater; collection; preservation; time interval; analysis of arsenic