Evaluating Potential Health Effects of Secondary Drinking Water Contaminants.
The Agency for Toxic Substances and Disease Registry (ATSDR) evaluates the individual and combined health effects of exposure to contaminants found in private drinking water. ATSDR initially screens the environmental contaminant data with existing health comparison guidelines and water quality standards. Many contaminants found in private well water can be considered more of a nuisance for the consumer than a health issue.
The U.S. Environmental Protection Agency (U.S. EPA) has established nonmandatory, secondary drinking water standards for 15 of these contaminants known as Secondary Maximum Contaminant Levels (SMCLs). The main concern for these contaminants is that they might cause aesthetic effects (undesirable taste, odor, or color); cosmetic effects (such as skin or tooth discoloration); or technical effects (such as corrosion or staining of household plumbing or fixtures).
By law, U.S. EPA drinking water standards (both primary and secondary) are only applicable to public drinking water; however, they are often used as screening values to determine potential problems in private drinking water supplies. ATSDR's experience in addressing private well contamination indicates that while several metals with an SMCL might only appear as an aesthetic issue for the consumer, they can potentially be harmful at levels above the SMCL. Moreover, exposure to several of these secondary contaminants, when combined with other contaminants in the water, might have an enhanced adverse health effect. The case study that follows is an example of this water quality issue, along with ways to ensure safe drinking water.
Case Study: Pearce Creek Dredged Material Containment Area
The Pearce Creek Dredged Material Containment Area (DMCA) is located in Cecil County, Maryland. Several small communities border the DMCA (Figure 1) and residents rely on private wells to meet their household water needs.
The U.S. Army Corps of Engineers (USACE) disposed of dredged material (sediments) from the Chesapeake Bay and Delaware Canal into the Pearce Creek DMCA from 1937 to 1938 and then again from the 1960s to 1993. In response to concerns that contaminants from the DMCA were affecting nearby residential well water, USACE discontinued disposal of dredge material into Pearce Creek.
In 2012, the U.S. Geological Survey reported that contaminants from dredged material in the Pearce Creek DMCA had degraded local groundwater quality. Several metals detected in groundwater samples exceeded U.S. EPA primary or secondary drinking water standards. In 2013, follow-up sampling by the Cecil County Health Department confirmed that the concentrations of metals in many residential wells near the DMCA exceeded U.S. EPA drinking water standards.
In July 2014, the Cecil County Health Department requested ATSDR to address two specific health concerns regarding elevated levels of metals found in residential drinking water wells near the Pearce Creek DMCA:
1. Can exposure to individual contaminants (such as aluminum, manganese, and iron) at concentrations exceeding U.S. EPA SMCLs pose a public health hazard?
2. Are synergistic effects possible from exposure to multiple contaminants at concentrations exceeding SMCLs? That is, can the combined effect from exposure to a mixture of such contaminants be greater than the sum of the effects from exposure to the contaminants individually?
ATSDR's Site Evaluation
ATSDR evaluated water sampling data, collected between 1987 and 2013, from approximately 187 residential wells near the Pearce Creek DMCA. ATSDR assessed the exposures using ATSDR's public health assessment evaluation process and reviewed available scientific literature regarding the effect of chemical interactions on the overall potential adverse health effects of contaminant mixtures.
Health Effects of Secondary Contaminants Health guideline values, such as ATSDR minimum risk levels (MRLs) and U.S. EPA reference doses (RfDs) were used to evaluate potential health effects from exposure to hazardous substances in the drinking water. A health guideline value is an estimate of daily human exposure to a substance that is unlikely to cause harmful, noncarcinogenic health effects. For some secondary contaminants, MRLs and RfDs have not been established. We reviewed ATSDR's Toxicological Profiles and other toxicological information sources to estimate contaminant levels (or doses) that might cause adverse health effects. Contaminant-specific drinking water exposure doses for residential well users were estimated and compared to available health effect levels.
Some secondary contaminants, such as chloride, iron, and sodium, are also essential nutrients. For these contaminants, we compared drinking water exposure doses to the National Institute of Medicine's established tolerable upper intake levels, where available. These upper intake levels represent the highest level of daily nutrient intake from all dietary sources that is likely to pose no risk of adverse health effects to almost all individuals in the general population.
Mixture Effects (From Coexposure to Multiple Contaminants)
For possible synergistic effects from exposure to multiple contaminants at concentrations exceeding SMCLs and other ATSDR health comparison values, we first evaluated possible harmful health effects from exposures to individual contaminants. ATSDR determined that individual exposures to several contaminants found in drinking water might cause harmful, noncancer health effects, including
* gastrointestinal problems in children and adults (copper, iron, and sulfate);
* neurological, behavioral, or neurodevelopmental effects in children (aluminum, lead, and manganese); and
* neurological effects in adults (aluminum and manganese).
Scientific literature on nervous system effects from coexposure to aluminum, lead, and manganese, and gastrointestinal effects from coexposure to copper, iron, and sulfate were inadequate to assess possible joint toxic interactions for these two contaminant mixtures. ATSDR conservatively assumed that the adverse effects were additive so that the potential hazard of each mixture can be estimated by summing the health hazard of the individual chemicals. Therefore, for individuals drinking water from residential wells near the Pearce Creek DMCA, the potential risk of neurological effects from exposure to mixtures of manganese, lead, and aluminum, or gastrointestinal effects from exposure to mixtures of copper, sulfate, and iron is likely greater than the risks that would be expected from exposure to any of these contaminants individually.
More detailed information on ATSDR's toxicological evaluation of contaminant mixtures for this site can be found in the documents referenced below (U.S. Department of Health and Human Services, 2016, 2017).
Impact of ATSDR's Public Health Conclusions and Recommendations
ATSDR concluded that drinking well water from some residential wells near the Pearce Creek DMCA could harm people's health, and individuals exposed to contaminant mixtures might have a greater risk of harmful effects than the risk that would be expected from exposure to any of these contaminants individually. ATSDR recommended that until homes are connected to the municipal water system, residents with private wells use bottled water for drinking and cooking.
In response to ATSDR's findings that private drinking water could harm people's health, the Maryland Department of the Environment announced that USACE and the Maryland Port Authority were providing bottled water free of charge to area residents until their homes are connected to the Town of Cecilton municipal water system (Figure 2.) These actions helped reduce potential harmful exposures to contaminated drinking water for more than 600 people living near the Pearce Creek DMCA.
Public health officials faced with a similar exposure scenario should be aware that harmful effects from water contaminants that are considered an essential metal or only a concern for aesthetic or other reasons, could be harmful if the levels are high enough and when the health effects of exposure to all contaminants in the water mixture are considered.
Please Note: Illustration(s) are not available due to copyright restrictions.
Editor's Note: As part of our continuing effort to highlight innovative approaches to improving the health and environment of communities, the Journal is pleased to publish a bimonthly column from the Agency for Toxic Substances and Disease Registry (ATSDR). ATSDR is a federal public health agency of the U.S. Department of Health and Human Services (HHS) and shares a common office of the Director with the National Center for Environmental Health (NCEH) at the Centers for Disease Control and Prevention (CDC). ATSDR serves the public by using the best science, taking responsive public health actions, and providing trusted health information to prevent harmful exposures and diseases related to toxic substances.
The purpose of this column is to inform readers of ATSDR's activities and initiatives to better understand the relationship between exposure to hazardous substances in the environment and their impact on human health and how to protect public health. We believe that the column will provide a valuable resource to our readership by helping to make known the considerable resources and expertise that ATSDR has available to assist communities, states, and others to assure good environmental health practice for all is served.
The conclusions of this column are those of the author(s) and do not necessarily represent the official position of ATSDR, CDC, or HHS.
Stephen Richardson is an environmental health scientist with ATSDR's Division of Community Health Investigations. He has more than 25 years of experience assessing potential health risks from human exposure to environmental contaminants.
Corresponding Author: Stephen (Steve) Richardson, Environmental Health Scientist, Agency for Toxic Substances and Dis ease Registry, Division of Community Health Investigations, Eastern Branch. E-mail: firstname.lastname@example.org.
U.S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry. (2016). Letter health consultation: Earleville private groundwater well quality, Pearce Creek Dredged Material Containment Area (DMCA), Cecil County, Maryland. Retrieved from https:// www.atsdr.cdc.gov/HAC/pha/PearceCreek/ Pearce_Creek_DMCA_LHC_05-27-2016_ 508.pdf
U.S. Department of Health and Human Services, Agency for Toxic Substances and Disease Registry. (2017). Health consultation: Evaluation of contaminants in residential drinking water wells near the Pearce Creek Dredged Material Containment Area (DMCA), Earleville, Cecil County, Maryland. Retrieved from https://www.atsdr.cdc.gov/HAC/pha/ PearceCreekDMCA/Pearce_Creek_DMCA_ Residential_Drinking_Water_Wells_Evalu ation_(MD)_HC_final_for_records_center_ 02-14-2017_508.pdf
Caption: FIGURE 1 Map of Pearce Creek Dredged Material Containment Area (DMCA) and Surrounding Areas
Caption: FIGURE 2 Location of Residential Areas Near the Pearce Creek Dredged Material Containment Area (DMCA) to Be Serviced by the Town of Cecilton Municipal Water System
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|Title Annotation:||DIRECT FROM ATSDR|
|Publication:||Journal of Environmental Health|
|Date:||Nov 1, 2017|
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