Abstract
Arsenic is naturally found in surface and ground waters and the inorganic forms of arsenic are the most toxic forms. The adverse health effects of arsenic may involve the respiratory, gastrointestinal, cardiovascular, nervous, and haematopoietic systems. Arsenic contamination in drinking water is a global problem widely seen in Bangladesh and West Bengal of the Indian sub continent. As there is a great demand for field test kits due to the anticipated reduction of the US EPA arsenic standard from 50ppb to 10ppb a field kit which offers rapid, simple and safe method for precise estimation of arsenic at 10ppb in drinking water samples is developed. Field methods, based on the mercuric-bromide-stain, consist of three different major parts, which are carried out stepwise. The first part of the procedure is to remove serious interference caused by hydrogen sulphide. In commercially available kits either the sulphide is oxidized to sulphate and the excess oxidizing reagent removed prior to the hydride generation step or, the hydrogen sulphide is filtered out by passing the gas stream through a filter impregnated with lead acetate during the hydride generation step. The present method employs cupric chloride in combination with ferric chloride or Fentonis reagent for the removal of hydrogen sulphide, which is rapid, simple and more efficient. Other interferences at this step of the analyses are normally not expected for drinking water analysis. In the second step, the generation of the arsine gas involves the classical way of using zinc metal and hydrochloric acid, which produce the enascenti hydrogen, which is the actual reducing agent. Hydrochloric acid can be replaced by sulfamic acid, which is solid and avoids a major disadvantage of having to handle a corrosive liquid in the field. The arsine gas produces a yellowish spot on the reagent paper. Depending on the arsenic content, either, Yellow n H (HgBr)2 As (10-50ppb), Brown n (HgBr)3 As (50-100ppb) or Black n Hg3 As2 (>100ppb) are formed which can be precisely estimated by visual comparison with standard color chart. The results obtained by field kits agree well with the data obtained through I.C.P.AES methods. The most important characteristic for field measurement is that analytical results can be obtained on the site where the sample is taken with high precision and can be conveniently utilized for monitoring arsenic rapidly in a highly contaminated large geographical area.
Highlights
Arsenic, a common contaminant of ground water, has been found to adversely affect human health at levels as low as 10 micro grams per liter
As most of the water samples from arsenic rich areas originate from reducing environments they are likely to contain various amounts of sulphur in its lowest oxidation state
Two methods to remove hydrogen sulphide are currently in use; either the sulphide is oxidized to sulphate and the excess oxidizing reagent removed prior to the hydride generation step or, as is done in the larger number of available kits, the hydrogen sulphide is filtered out by passing the gas stream through a filter impregnated with lead acetate during the hydride generation step
Summary
A common contaminant of ground water, has been found to adversely affect human health at levels as low as 10 micro grams per liter. The quantification of trace amounts of arsenic in water samples has always been a problem. The current methods rely on expensive apparatus, complicated procedures, and dangerous chemicals reagents [1] Low cost test kits, available in the past had a working range of 100 to 3000μg/L, which is not sensitive enough to monitor drinking water supplies. The method employed here addresses many of these problems. Field methods play an important role in environmental analytical chemistry. The most important characteristic for field measurement is that analytical results can be obtained on the site where the sample is
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