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Dr. Carol Weisskopf, Analytical Chemist, WSU
The past several weeks for Food and Environmental Quality Laboratory employees have been more interesting than usual. We became involved in a local well water contamination dilemma that had the potential to become a major public health problem. An employee at the WSU Prosser Irrigated Agriculture Research and Extension Center (IAREC) noticed discoloration of his well water. In trying to determine the cause, the governmental agencies he contacted suggested that he have the water analyzed. Chemical screens can be prohibitively expensive; the cost can be reduced substantially by narrowing down possibilities before sample submission. Experts in a wide variety of fields staff the Prosser station; two went to look at the area around the well. They noticed that some soil on the adjacent property looked peculiar, and that the oddness extended to the roadside.
The IAREC scientists then conducted a very sophisticated test: when they touched the dirt and spat on their hands, the dust turned yellow. Since this is not a typical response from normal soil, they collected some soil and sent it to us.
The First Puzzle
Identification of an unknown is frequently a difficult process. In this case, it was easy. We were assisted by the fact that we were dealing with a colored compound at high concentrations; we could see where it was going in various solvents and sample manipulations. It was also one of those days when all of the equipment was working as it should. Gas chromatography-mass spectrometry (GC-MS) of a sample extract produced no significant peaks. GC-MS is used most frequently for compound identification, because it produces a spectrum that can be matched by computer to spectra in libraries. However, a chemical must be volatilized easily into the gas phase for analysis. Liquid chromatography-mass spectrometry (LC-MS) indicated a single compound present at high concentrations with a molecular weight within the range typical of most pesticides. With LC analysis, the chemical only has to dissolve in the liquid phase for analysis. LC-MS is less useful in identifications, because the spectra depend on operating conditions and can vary widely.
For GC-MS identification, we needed to make the chemical volatile. LC-MS indicated that the volatility problem was not the result of an extremely high molecular weight (it wasn't too heavy). Highly polar compounds, such as alcohols and acids, are not very volatile. We knew the unknown was polar because it was water soluble. Because methylation can reduce polarity and increase volatility, we treated the extract with a strong methylating reagent.
GC-MS resulted in a single peak with a spectrum easily matched to one in the library. It will be no surprise to anyone familiar with pesticide colors and properties that our yellow, polar unknown was the herbicide dinoseb. In fact, it was one of the two compounds the IAREC scientists suspected.
Scientific instrumentation is fine, but experience and common sense can get you further, faster and cheaper. Sometimes you just have to spit on your hands. One thing instrumentation can do well is figure out how much of something is there. The soil contained dinoseb at 400 to 600 ppm (0.04 - 0.06%). A sample of water from the well the IAREC employee used contained 500 ppb dinoseb.
Industrial Bio-Test Returns
Dinoseb is classified as a nitrophenol (a type of alcohol). It was also the subject of an EPA emergency suspension of use in 1986 because of its toxicological effects (see next article ). The toxicological testing necessary for its original registration, and which had indicated it was safe, was evidently conducted by Industrial Bio-Test Laboratories (Rachel's Hazardous Waste News, 12/02/86, http://www.envirolink.org/pubs/rachel/rhwn002b.htm). When doubts arose about studies performed by Industrial Bio-Test, subsequent retesting resulted in the suspension. You may recognize Industrial Bio-Test from my article last month. This lab almost single-handedly caused implementation of EPA's Good Laboratory Practice standards. The potential link between poor toxicity testing and groundwater contamination via improper storage or disposal of suspended products was one consequence of fraudulent laboratory testing I hadn't previously considered. The coincidence between the subject of last month's newsletter column and a player in this month's chemical crisis was remarkable.
Determining the Extent of Contamination
As we were conducting our initial tests, the Washington State Department of Ecology (Ecology) was also focusing on the problem. As one can imagine, the area of groundwater contamination and the number of households with affected wells were of concern. We had received the soil sample on a Monday. By Friday, Ecology delivered eight water samples to us for analysis. One of these samples, taken from a well more than a mile from the first, contained dinoseb at 100 ppb. The residents had also collected a water sample a month before, when they noticed discoloration of their well water, and had stored it in their refrigerator. That water sample was also analyzed and contained dinoseb at 300 ppb.
Pesticides in groundwater are generally found at low concentrations, and analytical methods usually focus on achievement of low detection limits. Detection of dinoseb is not unusual. It was reported in 2% of the Central Columbia Plateau groundwater samples tested between 1992 and 1995 (USGS circular 1144). Concentrations ranged from 0.01 to 1 ppb. The Department of Ecology's own laboratory looks for dinoseb at a detection limit of 0.063 ppb. These low detection limits take time as well as skill. Sometimes it's smarter to be only good enough. We developed a method with a 2 ppb detection limit that was not only fast and accurate but so simple as to be idiot proof. This was our equivalent of spitting on our hands. One of the pleasures of our laboratory work is that we know what the data are to be used for. With a drinking water quality standard of 7 ppb and wells contaminated at 100 to 500 ppb, speed was more important than finesse; our detection limit was good enough. Ecology investigators agreed, and we proceeded with analyses.
The Second Puzzle
During the next eight days we looked at water from 100 wells. Fortunately, at press time only the two originally identified wells had been found to contain dinoseb at a concentration greater than 2 ppb. Because of our ability to give Ecology results from water analyses within 12 to 36 hours, the residents could be notified quickly that their water was uncontaminated. That the first well was contaminated was unsurprising; it was adjacent to a site of high-level soil contamination. The contamination source for the second well, more than a mile from the first, was more confusing. A number of wells between and around the two sites contained no detectable dinoseb. Department of Ecology sleuthing led to a transport hypothesis based on a highly unlikely concatenation of events. A water pipe near the contaminated site broke in winter. The water flowed for more than a month, flooding the site. Contaminated water ran into an empty irrigation canal. The irrigation system was filled with water in preparation for summer. Water flowed down a nearby irrigation diversion pipe and delivered contaminated water directly to the second well, which had a casing in poor condition. This rapid transit system accounting for recent, simultaneous contamination of two isolated wells by a substance that was banned 12 years ago may seem improbable. It has, however, been supported so far by sediment residue data and is probably the way it actually happened.
The story is not yet over. The landowner will clean up the
contaminated site. The Department of Ecology will install monitoring
wells and continue to monitor the area downstream of the irrigation
diversion pipe. However, after a week and two weekends of hard
work, Ecology and FEQL cooperation helped solve the contamination
riddle and assure affected individuals of the safety of their
water.
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