DACTHAL® GROUNDWATER CONTAMINATION
COLOMA TOWNSHIP, BERRIEN COUNTY, MICHIGAN
The mono- and di-acid metabolites of the herbicide Dacthal® have been detected in wells sampled in the Coloma Township area of Berrien County, Michigan (Figure 1). Many of the detections were at levels above the U.S. Environmental Protection Agency (U.S. EPA) Lifetime Health Advisory Level (LHAL) for Dacthal® of 70 parts per billion (ppb) and above the Michigan Department of Environmental Quality (MDEQ) Drinking Water Criterion (DWC) for Dacthal® of 73 ppb. How long the contamination has been present or where the source is located is currently unknown.
The contamination of the Coloma-area groundwater has been determined to be a current public health hazard. The MDEQ is working to establish the extent of contamination, and the Michigan Department of Agriculture (MDA) is ascertaining the source of contamination. Private affected well-owners are encouraged to continue using bottled water for drinking and cooking. Affected school and other public buildings must continue using bottled water per state and federal laws. Because affected private well-owners are not required to stop using their wells for drinking water purposes, the contamination presents an indeterminate future public health hazard. A safe supply of drinking water should be established for the township.
On June 20, 2001, the well installed in 1999 at Washington Elementary School (Figure 2) in Coloma Township, Berrien County, Michigan, was sampled by the U.S. EPA as part of a non-community water supply study. The school had been randomly chosen along with others in the state for this survey. Samples were analyzed for chemicals and contaminants not usually tested for in typical water tests. The mono- and di-acid metabolites of Dacthal®, a pre-emergent herbicide, were detected in the samples from the school but not in those taken from the other Michigan sites. The detections were at concentrations exceeding the LHAL, an estimate of acceptable drinking water levels for a chemical substance based on noncancer health effects. Confirmation testing at the school on July 31 revealed a level of 181 ppb (U.S. EPA laboratory) and 110 ppb (referee lab) total metabolites. The MDEQ informed the Berrien County Health Department (BCHD) of the results of the analyses and advised that the school use a different supply of drinking water. The school has been using bottled water since September 7, when school officials were apprised of the situation. Parents of schoolchildren have been notified of these actions (Moser 2002, Pigg 2002a).
Coloma Township is described as a "resort-type, bedroom community" with a population of 5,217 according to the 2000 Census. Many of the local manufacturers are agriculture-related (www.colomatownship.org ). Michigan Nurseries, LLC (formerly DeGroots Nursery) is located in the northern section of the area under investigation.
Dacthal® (dimethyl tetrachloroterephthalate) is registered for use on many vegetables, landscape plants, and turf. According to agrochemical distributors, its current primary use in southwest Michigan is on strawberries (M. Hansen, MDA-Pesticide and Plant Pest Management Division, personal communication, 2002).
The MDEQ has begun "envelope" sampling to determine the areal extent of contamination. Field staff started with the wells closest to the school and are working their way outward. Well-owners with contaminated wells have been advised to use bottled water for drinking and cooking until a safe water source can be established. The MDEQ has asked the Michigan Department of Community Health (MDCH) to provide health effects information about Dacthal® exposure to the citizens of the township. The MDA is investigating the possible source of contamination.
The sampling results in this consultation were taken from the available investigations of the property, and are not adjusted for limitations or bias in the sampling programs. The MDEQ criteria used in the current health consultation are the DWC and the Groundwater Household Use Screening Level (GHUSL). The Agency for Toxic Substances and Disease Registry (ATSDR) Comparison Value used is the Reference Dose Media Evaluation Guide (RMEG).
The DWC is a level in groundwater that is considered safe for long-term daily consumption. Adverse aesthetic impacts (taste and/or odors) are taken into account for some hazardous substances. Residential DWC are protective of both adults and children who might live on the property. This criterion is only used if groundwater is currently used as a source of drinking water or could be used as drinking water in the future.
The GHUSL is a level in groundwater that is protective of dermal exposure while bathing or showering and of inhalation exposure to contaminants that vaporize during household activities such as bathing and dish or clothes washing. The GHUSL is considered when groundwater has been replaced by an alternative source of drinking water but other residential household uses of groundwater continue until a permanent replacement water supply is provided.
The RMEG represents a concentration of a noncarcinogenic substance in water, soil, or air to which humans may be exposed long-term without experiencing adverse health effects. Unless ruled out by the exposure scenario, it is assumed that children are exposed to the substance. The Child and Adult RMEGs for Dacthal® are 100 and 400 ppb, respectively. The value serves only as a screening value and, if exceeded, does not necessarily indicate a public health hazard. When an RMEG is exceeded, further evaluation of toxicity data and exposure scenarios is required before determining public health conclusions.
In the initial phase of envelope sampling, six wells, including the school well, were sampled on September 10, 2001 by MDEQ Drinking Water and Radiological Protection (DWRP) staff. All samples tested positive for the Dacthal® metabolites, with the sample from the school reporting 91 ppb. Subsequent testing, expanding outward from the school, has revealed more impacted wells. Detections have occurred at various well depths. There is not geographic trend, meaning that the hotspots found thus far have not indicated a pattern that would suggest a point source of contamination. Well-owners with contaminated wells have been advised not to use the water for drinking or cooking. The MDEQ has offered to provide bottled water to these people (Pigg 2002a). Envelope monitoring will continue at 48 wells every two weeks until boundaries to the contamination have been determined (Pigg 2002b). The table below provides a to-date summary of testing results.
|Total number of wells tested to date (04/29/2002)||450|
|Number of detections (detection limit = 1 ppb)||225 (92 pending)|
|Range of concentrations (not including non-detects)||1-556 ppb|
|Number of U.S. EPA LHAL exceedances||27|
|Number of MDEQ DWC exceedances||27|
|Number of Child RMEG exceedances||16|
|Number of Adult RMEG exceedances||1|
Human Exposure Pathways
To determine whether nearby residents are, have been, or are likely to be exposed to contaminants associated with a property, the Agency for Toxic Substances and Disease Registry (ATSDR) and MDCH evaluate the environmental and human components that could lead to human exposure. An exposure pathway contains five major elements: (1) a source of contamination, (2) contaminant transport through an environmental medium, (3) a point of exposure, (4) a route of human exposure, and (5) an exposed population. An exposure pathway is considered a complete pathway if there is evidence that all five of these elements are, have been, or will be present at the property. Alternatively, an exposure pathway is considered complete if there is a high probability of exposure. It is considered either a potential or an incomplete pathway if there is no evidence that at least one of the elements above are, have been, or will be present at the property, or that there is a lower probability of exposure.
The primary route of exposure to Dacthal® or its metabolites in the Coloma Township area is oral via ingestion of contaminated groundwater. Dacthal® was originally registered for general use in 1958 (U.S. EPA, 1998). How long the herbicide or its metabolites have been in the groundwater in the affected area is currently unknown. Therefore, it is unknown how long and to what levels previous and current users may have been exposed. If currently exposed residents choose not to switch to bottled water for drinking and cooking purposes, or if other, as yet unidentified, wells are contaminated, exposure could continue indefinitely and residents could experience health effects.
Some currently exposed residents are apparently choosing not to use bottled water. Current DWRP records indicate that only 119 households, out of the 225 with positive test results, are receiving bottled water deliveries. The remaining 106 households have not responded to MDEQ's offer of bottled water (C. Rubitschun, MDEQ-DWRP, personal communication, 2002). During the sampling performed in January, a resident told the sampling staff that even if her water were contaminated, she would not switch (C. Bush, MDCH, Dacthal Groundwater Contamination file, 2002). As well, a letter to the editor of the local paper indicated that he felt the contamination was a hoax and that "taxpayers are being forced into this city water issue for possible financial reasons" (Kowerduck 2002). For these reasons and because the extent of contamination is not yet known, it is likely that exposure is continuing for some residents of the area.
Future residents of existing homes should obtain information about a contaminated well in a disclosure required with the sale. Future residents of new homes should not be at risk for exposure because a moratorium on well-drilling is pending until the MDEQ and the county health department determine appropriate actions (C. Rubitschun, MDEQ-DWRP, personal communication, 2002).
The DWC for Dacthal® is based upon the U.S. EPA Reference Dose (RfD). The RfD is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily exposure to a human adult that is likely to be without an appreciable risk of adverse health effects during a lifetime. The RfD for Dacthal®, 0.01 mg/kg body weight per day, is based on effects on the lungs, liver, kidney, and thyroid in rats (U.S. EPA 1994). If a person were receiving all of their drinking water from a contaminated well, then a 70-kg adult drinking two liters of water per day at the maximum concentration of Dacthal® found in the Coloma area would be exposed to 0.016 mg/kg of body weight per day. The U.S. EPA has listed Dacthal® as a possible carcinogen (U.S. EPA 1998) based on an increased incidence of thyroid tumors in both sexes of the rat and liver tumors in female rats and mice. Since Dacthal® and its metabolites were detected above the DWC, people drinking the water could experience health effects.
The two metabolites of Dacthal® are 2,3,5,6-tetrachloroterephthalic acid (TPA) and monomethyl-2,3,5,6-tetrachloroterephthalate (MTP), or the di- and mono-acids, respectively. It is the TPA metabolite that is found most frequently in the environment after Dacthal® use (U.S. EPA 1998). Soil metabolism converts Dacthal® to TPA, which is known to leach through soil and pollute groundwater. Animal studies performed on the di-acid concluded that TPA did not cause adverse health effects except in one case, which showed a weak chromosomal effect at a very high dose, but this did not indicate appreciable concern (CDPR 1994). Therefore, it can reasonably be expected that the TPA metabolite is no more toxic, and is probably less toxic, to humans than the parent compound. However, as stated earlier, since Dacthal® and its metabolites were detected above the DWC, people drinking the water could experience health effects.
Hexachlorobenzene (HCB) and polyhalogenated dibenzo-p-dioxins and dibenzofurans (collectively referred to as dioxin) are recognized impurities of Dacthal®. The RfD for each of these compounds is 0.8 and 0.000001 µg/kg body weight per day, respectively (U.S. EPA 1996, 1998). The maximum level of HCB allowable in formulations of Dacthal® is 0.3 percent. The dioxin reported in Dacthal® formulations is 0.1 ppb, which is equal to 0.00000001 percent. The concentration of Dacthal® would have to be 5,333 ppb in order for the RfD of HCB to be exceeded. No HCB has been detected in 14 high-Dacthal® wells tested for a more extensive list of possible contaminats (Pigg 2002c). At the maximum concentration of Dacthal® currently in the Coloma-area groundwater (556 ppb), a person would have to drink more than 1,250 liters of water per day in order for the RfD of dioxin to be exceeded via this exposure route. The physical properties of both of these compounds suggest that they would more likely bind to soil than to water. Therefore no adverse health effects are expected to occur as a result of HCB or dioxin contamination of the Dacthal® found in the Coloma-area groundwater.
Because the known concentrations of Dacthal® in the Coloma-area groundwater do not exceed the GHUSL of 590 ppb, dermal contact with and inhalation of vapors of heated groundwater, such as would be expected when washing dishes or bathing, do not represent a hazardous exposure to people using affected wells.
ATSDR Child Health Initiative
Children may be at greater risk than adults from exposure to hazardous substances at sites of environmental contamination. Children engage in activities such as playing outdoors and hand-to-mouth behaviors that could increase their intake of hazardous substances. They are shorter than most adults, and therefore breathe dust, soil, and vapors closer to the ground. Their lower body weight and higher intake rate results in a greater dose of hazardous substance per unit of body weight. The developing body systems of children can sustain permanent damage if toxic exposures are high enough during critical growth stages. Even before birth, children are forming the body organs they need to last a lifetime. Injury during key periods of growth and development could lead to malformation of organs (teratogenesis), disruption of function, and premature death. Exposure of the mother could lead to exposure of the fetus, via the placenta, or affect the fetus because of injury or illness sustained by the mother (ATSDR 1998). The obvious implication for environmental health is that children can experience substantially greater exposures than adults to toxicants that are present in soil, water, or air.
The Child RMEG for Dacthal® was exceeded in 16 samples. The well at the school exceeded the DWC. There are several homes in the area used as daycare facilities. Therefore, children in the Coloma Township area may be exposed to Dacthal® in the groundwater. However, there are no studies available of Dacthal® or its metabolites that used young animals to determine how they might be affected as compared to effects seen in adult animals.
Under current conditions and based upon the ATSDR Public Health Assessment Guidance Manual criteria (ATSDR 1992), the contamination of the Coloma-area groundwater by Dacthal® and its metabolites presents a public health hazard. Exposure to Dacthal® has occurred and will continue to occur until the extent of contamination is determined and those people exposed use bottled water for drinking purposes. Current concentrations indicate a potential for adverse health effects if exposure continues long-term. It is unknown how long exposure has occurred, or to what concentrations people may have been exposed in the past.
Because residents with affected wells are not required to stop using those wells for drinking water purposes, the future public health hazard is indeterminate. Although the persistence of TPA in groundwater is not known, indications are that it is quite persistent (U.S. EPA 1998). Selling an existing house or building a new one requires that the structure be supplied with safe drinking water.
- Those whose wells have tested positive for Dacthal® should drink and
cook with bottled water.
- The MDEQ should continue to sample the groundwater in Coloma Township to determine the full extent of contamination. Those wells which have not been shown to be contaminated with Dacthal® should be retested by MDEQ regularly to determine if they subsequently have become contaminated.
- The MDA should continue its investigation into the source of the contamination and initiate legal or administrative procedures against any potentially responsible parties, according to the powers granted by state law.
- Well-owners with affected wells should be notified of their individual analysis results and offered bottled water, as per MDEQ protocol. This action is already underway.
- The local health department should maintain a moratorium on well-drilling until information is provided by the MDEQ regarding the extent of contamination and any clean-up procedures.
- Coloma Charter Township officials should take steps to assure a safe drinking water supply for the community. The officials should coordinate these efforts with MDEQ and the local health department. State funding has already been approved to begin extending public water from the city of Coloma to Washington Elementary School and to start feasibility and design studies on supplying public water to affected areas of the township (Pigg 2002c).
- Subsequent to any public meetings, MDCH will provide any necessary follow-up information. Township officials should see that these materials are accessible to all residents via the township website, a public repository, or other means. Appendix A contains the follow-up information provided following the public meeting of January 24, 2002 and addresses other citizen concerns.
- It is not recommended at this time that a health study be conducted on persons who may have been exposed to the contaminated groundwater. However, future information regarding residents' health could change this recommendation.
The MDCH will be available to consult on the appropriateness and efficacy of future remedial actions.
If any citizen has additional information or health concerns regarding the Dacthal® groundwater contamination in the Coloma Township area, please contact the Michigan Department of Community Health, Environmental Epidemiology Division, at 1-800-648-6942.
Michigan Department of Community Health
Christina Bush, Toxicologist
Robin Freer, Resource Specialist
ATSDR Regional Representative
Regional Services, Region V
Office of the Assistant Administrator
ATSDR Technical Project Officer
Division of Health Assessment and Consultation
Superfund Site Assessment Branch
ATSDR. 1992. Agency for Toxic Substances and Disease Registry. Public Health Assessment Guidance Manual.
ATSDR. 1998. Agency for Toxic Substances and Disease Registry, Division of Health Assessment and Consultation. Guidance on Including Child Health Issues in Division of Health Assessment and Consultation Documents. July 2, 1998.
California Department of Pesticide Regulation (CDPR). 1994. Summary of Toxicology Data. Chlorthal-dimethyl (DCPA). Medical Toxicology Branch.
Kowerduck, R. 2002. Tri-City Record, Letter to Editor. February 6, 2002. http://www.tricityrecord.com/feb_06_2002_letters.htm
Moser, M. 2002. "Basic Information regarding the Dacthal/DCPA Contamination Problem Discovered in Coloma Charter Township." Included with Public Meeting Notice dated January 14, 2002
Pigg, R. 2002a. "Draft Summary of DCPA Groundwater Contamination Investigation in Coloma Township, Michigan." MDA Groundwater Monitoring Program. January 8, 2002.
Pigg, R. 2002b. "Notes on Coloma DCPA Contamination Workgroup Meeting." MDA Groundwater Monitoring Program. January 9, 2002.
Pigg, R. 2002c. "Update of Dacthal (DCPA) Contamination Investigation for Coloma township Residents: April 30, 2002." MDA Groudnwater Monitoring Program. April 30, 2002.
U.S. EPA. 1994. IRIS Summary: Dacthal (CASRN 1861-32-1). Integrated Risk Information System.
U.S. EPA. 1996. IRIS Summary: Hexachlorobenzene (CASRN 118-74-1). Integrated Risk Information System.
U.S. EPA. 1998. Reregistration Eligibility Decision (RED): DCPA. Office of Prevention, Pesticides and Toxic Substances. EPA 738-R-98-005. November 1998.
Note: Unless otherwise indicated, Dacthal® and its metabolites are used interchangeably.
Questions received at Public Meeting 1/24/02
Could fish in area lakes become contaminated?
It is unlikely that Dacthal® will accumulate in fish tissue in surface waters containing the herbicide. The biochemical nature of Dacthal® indicates that animals excrete it readily. The reason you see fish advisories for mercury, PCBs, and other compounds is because those chemicals "prefer" to accumulate in the body tissue, usually the fat, of the fish and may be ingested when you eat the fish.
Will filtering my water (reverse osmosis, charcoal filtration, etc.) remove
The Department of Environmental Quality (DEQ) does not support treatment devices as a long-term safe alternate water source. Devices might not be maintained properly, especially should a house change hands, and could cause more health concerns from bacterial contamination and colonization of the device. Also, filtering devices may give a false sense of security to wellowners. The DEQ Drinking Water and Radiological Protection Division can discuss this issue in more detail.
Is there a risk of using contaminated water in humidifiers?
If contaminated water were to be aerosolized in a humidifier, any risk associated with inhaling that aerosol is minimal. The exposure route of primary concern is oral (eating or drinking).
Is there a risk to children from swimming in area lakes/rivers?
At the concentrations seen in the Coloma Township area, there is no risk posed to children or adults swimming in area waters. The Groundwater Household Use Screening Level (GHUSL), which is protective of body contact, is 590 parts per billion (ppb) and so far the highest groundwater concentration has been 253 ppb. Any Dacthal® metabolite entering surface water would be diluted in the volume of that water body. The Dacthal® parent compound itself would be broken down to the metabolites by sunlight and warm temperatures.
There is always the possibility of accidental (incidental) swallowing of the water when swimming. However, the amount swallowed would be minimal and would not greatly add to overall exposure.
Can I use contaminated water on my garden?
You can water your garden with groundwater containing Dacthal®. This herbicide was registered for use on numerous crops. You could also wash off your produce with this water and shake off the excess water - the amount of water remaining would barely, if at all, increase any exposure. If you feel unsure about using the groundwater for washing the produce, use bottled water.
When washing dishes in hot water, is the exposure greater?
Immersing your hands in hot water might make your skin more likely to absorb contaminants. In this case, it is unlikely that your skin would absorb any Dacthal® in hot water at current concentrations. (This would apply also to showering and bathing.) Nonetheless, wearing dish gloves when washing dishes is a precaution you should consider for general safety (e.g., protection from sharp knives, broken glass, and scalding water).
What about washing your hands if you have a cut?
Although contaminants can enter the body through a cut, the amount of time that your hands would be exposed to the water when washing (or any cut when bathing or swimming) would be minimal and would not greatly increase your exposure. (Also, Dacthal® is not a germ which can enter a cut and then, if conditions are right, start multiplying and result in an infection.) In this case, the benefits of hand-washing and other hygienic practices outweigh any risk associated with Dacthal®-contaminated water.
Will boiling water disable or break down the Dacthal®?
It is unknown what happens to Dacthal® when contaminated water is boiled.
Are there any health studies planned for the community, to see if there
is a higher-than-normal incidence of disease?
Currently, no health studies are planned to determine if there is an abnormal amount of specific medical diagnoses, such as cancer or non-cancerous diseases, in the township. The document, "Citizen's Guide for Community Health Studies," has been forwarded to the Coloma Township office for citizens' review to understand how various health studies are performed and what they can or cannot tell you.
Are there any medical tests to determine if you've been exposed to Dacthal®?
No, nor would results be able to predict what could be expected to happen regarding the exposed person's health.
Is the level of concern, 70-73 ppb, safe for daily use?
The EPA Lifetime Health Advisory Level, 70 ppb, is based on noncancer health effects. As indicated, it is considers exposure over a lifetime. The DEQ criterion, 73 ppb, more specifically indicates that the exposure duration is assumed to be 30 years. (This represents the national upper-bound, not average, time spent at one residence. This assumption incorporates conservatism and protection into the calculation.)
These levels also assume that not all of the exposure will occur via drinking contaminated groundwater, which adds more conservatism and protection into the numbers. If it were assumed that all of the exposure did occur via drinking contaminated groundwater, then the advisory/criterion values would be higher because there would be greater confidence in knowing the actual amount to which a person was exposed. Since, in this case, most, if not all, of the exposure is through the groundwater, 70-73 ppb is very protective.
While up to these levels might be considered "safe," the concern with finding a contaminant in the groundwater is that the aquifer has been shown to be vulnerable, meaning that other potentially harmful chemicals could enter the groundwater. This is why it has been recommended that any well-owner with a positive-test well, whether the concentration is above or below the level of concern, start using bottled water. Also, the concentration reported to you was a snapshot in time: the levels could decrease or increase.
Additional questions, received via phone or e-mail
Will Dacthal® show up in breastmilk?
In some animal studies, cattle were fed Dacthal® in the diet and about 0.1% of the dose they received ended up in the milk. If humans process Dacthal® in the same manner, then one one-thousandth of the concentration consumed by a nursing mother could show up in her milk. While this is certainly a much smaller dose to the infant, children are usually considered to be more susceptible to the effects of chemicals. There are no studies that were done on young animals in order to compare what might happen in them with what happens in adult animals. However, because of the protection built into the Health Advisory Level and the DEQ criterion, it is doubtful that any significant risk exists to the nursing infant. In this case, the benefits of breastfeeding a child outweigh any risk there might be of very low amounts of Dacthal® being present in the milk.
What kind of health concerns should those undergoing surgery have in regards
to drinking their water?
If the well is known to be contaminated with Dacthal® or if it has not been tested yet and you have a concern, then bottled water should be used for drinking and cooking. If you drink Dacthal®-contaminated water following surgery, it should not interfere with the healing process. You might want to discuss this with your doctor - he or she is the best judge of your medical situation.
If there is Dacthal® in my drinking water, could it be causing the sores
in and on my mouth?
According to the scientific research, there is no indication that Dacthal® would cause these sores.
This Dacthal® Groundwater Contamination Health Consultation was prepared by the Michigan Department of Community Health under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health consultation was begun.
Alan W. Yarbrough
Technical Project Officer, SPS, SSAB, DHAC, ATSDR
The Division of Health Assessment and Consultation, ATSDR, has reviewed this public health consultation and concurs with the findings.
Chief, State Programs Section, SSAB, DHAC, ATSDR