Perchlorate is well-known to pose risks for both human health and wildlife and has been shown to arise from many natural and anthropogenic sources, including ammonium perchlorate and lightning discharges. Wilkin and his colleagues sampled water from Wintersmith Lake, Oklahoma, before and after firework displays in July 2004, 2005, 2006 and in November 2005.
Their results indicated that within 14 hours of the displays, the background levels of perchlorate increased sharply 24-1028 times and typically peaked at 1 day, after which they slowly degraded until they reached normal levels within 20 to 80 days. Since the perchlorate disappearance rate seemed to mirror previously recorded microbial degradation rates and was also temperature dependent, they decided to test whether microbes were directly involved in a laboratory setting. They found that the microbes taken from the lake degraded the perchlorate whereas sterilized samples of lake water displayed no change in levels of the chemical. They concluded that the microbes preferred to use nitrate for food first before beginning to consume perchlorate.
Purnendu Dasgupta, a perchlorate expert from the University of Texas, Arlington, believes that the gradual degradation of perchlorate levels may be due instead to diffusion. To evaluate this hypothesis, Dasgupta suggests the use of several trace heavy metals whose concentrations also rise during firework displays as tracers. "If perchlorate disappeared but this tracer concentration remained stable, one could follow the argument with greater faith that it just did not disappear by dilution into deeper waters," he says.
Andrew Jackson, an environmental engineer and perchlorate expert at Texas Tech University, think that the study "helps to emphasize the fact that perchlorate exposure is not always from a well-documented contamination issue." He cites several transient sources, such as bleach or certain herbicides, as potential "exposure sources."
Todd Anderson, an environmental toxicologist from Texas Tech University, describes the study's value thusly: "The real impact of it is in helping to fill data gaps in our understanding of potential sources of perchlorate to the environment."
See also: ::The Prettiest Pollutants, ::Green Fireworks Come in All Colors, ::China's Environment Getting Worse... Before It Gets Better?, ::China Issues World's First 'Green GDP': Pollution Cost $64 Billion in 2004 (At Least), ::When the Waters Recede, Let There Be Green, ::What's in the Water? Ask the National Tap Water Quality Database