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This paper describes a modified procedure for the determination of nitrate in sediments and some natural water samples. In the Water Quality Branch Laboratories where large numbers of samples are regularly analysed, it was found that existing methods1,4 do not give precise and accurate results particularly when applied to sediment samples and some natural waters. The reasons for such inaccuracies have sebsequently been found and a method for removal of such interfering substances have been devised. The proposed method essentially consist of two steps. In the first step the interfering substances such as sulfide and humic acid substances are removed by precipitation with copper. The resultant solution is then analysed by a colorimetric approach utilizing cadmium fillings as the reducing agent to reduce nitrate to nitrite, and analyse the resultant nitrite with sulfanilamide, and naphtylene diamine. The smallest amount of nitrate that can be detected with certainty is approximately 10 mug-at N/Kg and 50 mug/ at N/Kg in water and sediments respectively. The figures for sediments are based on dissolving 20 gms. of sediment, dry weight, in 100 ml volume. The proposed method has been tested on a wide variety of natural water samples, sediments, clays and sands.

The paper deals with some results of work done in the USSR to establish maximal allowable doses (MAC) for the carcinogenic hydrocarbon benza(a)pyrene in human environment. At the same time it is a brief review of some discussions on this item which took place in USSR and on the international level.