A study of chlorates in Malta's environment

Abstract

The objective of this research was to determine the extent of occurrence of perchlorate and chlorate contamination in the Maltese environment in different matrices including water (drinking, ground and rain water), dust (inhalable and settleable dust), soils, algae and sea water samples. Perchlorate and chlorate were determined by ion chromatography following extraction from the different matrices. Perchlorate and chlorate were detected in 52 % and 29 % of drinking water samples collected during 2012 and 2013. Perchlorate was detected in ground water samples collected during April '12' and July '12' with mean concentrations of 0.83 µg L-1 and 1.1 µg L-1 respectively. Higher concentrations of perchlorate and chlorate were detected in surface runoff samples collected during 2012 (n=5) and 2013 (n=6), with both of these contaminants detected in all but one of the samples. Perchlorate concentrations in surface runoff ranged from below detection limit (BDL) to 129 µg L-1 , while chlorate concentrations ranged from BDL to 939 µg L-1 . Dust fall was collected during 11 different months ranging from September 2011 till February 2013, sampled from 44 different localities. Both perchlorate and chlorate displayed temporal and seasonal variations. The highest mean perchlorate concentration in dust fall was detected during July '12' (120 µg g-1 ), followed by August '12' (37 µg g- 1 ), and September '11' (17 µg g-1 ), while the lowest concentrations were detected in samples collected during February '13' (1.2 µg g1 ) and March '12' (0.48 µg g-1). The highest chlorate concentration was also detected in dust fall collected during July (43 µg g-1), however, the trend was not as clear as that observed for perchlorate, since the next highest concentration was detected in February rather than August. There was a significant correlation between perchlorate and chlorate concentrations in dust fall samples, which might imply that these have the same source. There was also a significant difference in chlorate and perchlorate concentrations in dust fall samples collected during different months and from different localities. The dust fall samples were analysed by X ray fluorescence and the content of the major elements, namely, Ca, Si, Fe, Al, Mg, K, Ti and P were obtained following calibration using standard mixtures made in house. The results indicate that the major component of dust fall is from local rock however there appears to be a trans-boundary component. The concentrations of perchlorate and chlorate in soils collected locally were lower than the concentrations detected in dust fall, with mean concentrations of 49.9 ng g·1 and 36.8 ng g· 1 respectively. High perchlorate concentrations were detected in algae ( Ulva lactuca) samples collected from 5 different localities with concentrations ranging from 1.34 µg g· 1 to 5.90 µg g· • All 5 sea water samples analyzed had perchlorate concentrations below detection limit. The results of this research have shown that perchlorate and chlorate concentrations have seasonal fluctuations, with the highest concentrations during the Summer months. Since the concentration of these two contaminants was not evenly distributed and was affected by seasonality, this shows that the main source of chlorate and perchlorate is anthropogenic. Since high concentrations of both perchlorate and chlorate were detected during the festive season, their main source is attributed to fireworks. The only known source of perchlorate in Malta is for the manufacture of pyrotechnic articles burned locally. Even though the highest perchlorate concentrations were detected during the festive season, perchlorate was detected in dust fall samples collected throughout the year. This means that perchlorate contamination presents a perennial problem. From exposure evaluation calculations it is reasonable to conclude that children are the most susceptible category of the population.