IDENTIFICATION OF ARSENIC LEVELS1N SRI LANKAN GROUNDWATERS AND DEVGLO•PMENT OF LOW-COST ARSENIC REMOVAL METHO'DOLOGY

Abstract

Arsenic. which is highly toxic to humans even at low concentrations is a dominant tracepollutant found in drinking water. Sri Lannkan standard (SLS 614,1983) for drinking water is 50ppb whereas WHO and proposed USEPA standard are 10 ppb. Arsenic originates both fromnatural and anthropogenic sources. Acute short-term exposure to high doses of arsenic can causeadverse health effects. Most commonly reported symptoms of chronic arsenic exposure areconjunctivitis, melanosis, hyperkeratosis and some other skin lesions. In severe cases, gangrenein the limbs has also been observed

In our region, Bangladesh is facing a severe pollution of drinking water due to arsenic. Thisarsenic derives from the geological strata underlying Bangladesh. The effect became dominantdue to large drops in groundwater levels. Due to Farakka darn, on the river Gangas in India,groundwater level is being lowered markedly during the dry season in the Northwestern andWestern regions of Bangladesh, exposing the dry sediment layer to oxidation. As a result, pyriteshave been dissolved in groundwater releasing arsenic into drinking water supplies.

In Sri Lanka also groundwater consumption and construction of darns across rivers areincreasing. Within the last twenty years many large darns were constructed. Therefore highdrawdown of water table in downstream areas of these darns may lead to problems similar toBangladesh since the geological aspects are similar (pyrites are found in calcipyres and graphite-bearing veins in Sri Lanka (Cooray, 1984». Hence the problem may exist in Sri Lanka, thoughit is not reported yet. One reason for absence of such data is the lack of facilities to measurearsenic. Therefore in this research the basic data on arsenic levels and its spatial variation inaquifers in Sri Lanka are being obtained. To reliably analyze the arsenic level in water, a methodbased on the Hydride Generation -Atomic Adsorption Spectrometry (HG-AAS) is beingdeveloped at the Faculty of Engineering, University of Peradeniya.

Most of the available arsenic treatment technologies perform well at high cost. It is important todevelop a low-cost treatment method for low-income countries. Presently SORAS method,introduced by a Switzerland-Bangladesh joint research group (Wegelin et al., 2000), is used athousehold level to treat drinking water. In this study a new low cost treatment method forarsenite, As (III) removal by sorption on laterite, has been researched. Laterite found abundantlyin South-western Sri Lanka contains iron. Mainly As (III) will be studied due to its high toxicity,mobility and solubility than arsenate, As (Y).

Also as a part of this study, the adsorption behaviour of arsenite on goethite was studied. Whenreviewing past studies it was found that many studies have been carried out on arsenate removalusing goethite. There have been fewer experiments on arsenite removal. Almost 90% arseniteremoval could be achieved using goethite and the high removal was observed within the naturalpH range. This will lead to an efficient arsenite removal process from the natural water since nopH adjustment is needed.