ADDENDUM to PUBLIC HEALTH ASSESSMENT
DOVER MUNICIPAL LANDFILL
DOVER, STRAFFORD COUNTY, NEW HAMPSHIRE
When conducting an ATSDR public health assessment, healthassessors identify and review all available environmentalcontamination data for a site. The on- and off-site portions ofthis section describe sampling that has been done and identifycontaminants of concern. The following is a discussion of theprocess ATSDR uses for selecting contaminants of concern andToxic Chemical Release Inventory (TRI) data.
Selection of Contaminants of Concern
ATSDR selects contaminants for further evaluation based upon thefollowing factors (12):
|(1)||comparison of concentrations of contaminants on andoff site with media values for noncarcinogenic andcarcinogenic endpoints,|
|(2)||sampling plan and field and laboratory data quality, and|
|(3)||community health concerns.|
Identification of a contaminant of concern in the On-site andOff-site Contamination subsections does not mean that exposurewill result in adverse health effects, only that additionalevaluation is necessary. The public health significance, if any,of exposure to the contaminants of concern is evaluated insubsequent sections of the public health assessment.
Comparison values are used to select contaminants for furtherevaluation. The ones used in this public health assessment wereATSDR's Environmental Media Evaluation Guides (EMEGs) and CancerRisk Evaluation Guide (CREG), and EPA's Reference Doses (RfD),Maximum Contaminant Levels (MCLs), lifetime drinking water healthadvisory (LTHA), and drinking water action level for lead (AL). Both carcinogenic and noncarcinogenic endpoints were consideredin selecting contaminants of concern.
EMEGs are media-specific estimates of exposure levels that pose aminimal risk to humans. They are based on ATSDR's minimal risklevels (MRLs). When a MRL is not available for a substance, anEPA RfD, if available, is used to estimate media-specificexposure levels. CREGs are estimated contaminant concentrationsbased on a one excess cancer in a million persons exposed over alifetime. CREGs are calculated from EPA's cancer slope factors. MCLs represent contaminant concentrations that EPA deemsprotective of public health (considering the availability andeconomics of water treatment technology) over a lifetime (70years) at an exposure rate of 2 liters of water per day. LTHAsare similar to MCLs except that only health factors areconsidered. The availability and economics of water treatmenttechnology is not. Exceeding the EPA drinking water AL for leadindicates that further evaluation of the possible healthconsequences of exposure to lead should be done. Especiallyimportant would be the identification of possible sources ofexposure.
Review of Toxic Chemical Release Inventory (TRI) Data
To identify possible facilities that could contribute tocontamination near the Dover Municipal Landfill Site, the NH DPHSsearched the 1987 and 1988 Toxic Chemical Release Inventory(TRI). The TRI is developed by EPA from the chemical releaseinformation provided by certain industries. A search of the TRIdid not contain information on toxic chemical releases in thesurrounding towns of Barrington, Durham, Lee, Madbury, andRollinsford, NH (see Appendix I). Information on toxic chemicalreleases to the air was found during a search of the TRI forfacilities in the cities of Dover, Portsmouth, Rochester, andSomersworth and in the surrounding town of Newington. A toxicchemical release to water was also found in the 1987 TRI for onefacility in the City of Rochester. Although some of the toxicchemicals released to the environment from the facilities listedin the TRI may be contributing to ambient air quality at andaround the site, previous site investigations have indicated thatonly emissions of volatile organic compounds (VOCs) from theleachate swale into the surrounding air may present increasedhealth risks for residents living near the site.
A. On-Site Contamination
The FS and ROD contained sampling data for groundwater from 1990. Those data are presented in Table 4 (6,7). In general, thecontaminant levels are lower than those from 1986 and 1987 (seeTable 1 in the original public health assessment).
B. Off-Site Contamination
In 1990, EPA conducted one 8-hour sampling of the air at fivelocation on or around the Dover Landfill site (6). Four of thelocations were selected to determine maximum levels ofcontaminants being emitted from the leachate into the air and theother was chosen to represent background. The concentrationsdetected were somewhat lower than those for off-site samplingdone 1986 and 1987 (see Table 3 of the original public healthassessment). The air sampling in 1990 is not useable inpredicting possible human health hazards because only one day ofsampling was done and no attempt was made to determine localmeteorologic conditions.
Sampling of eight private drinking water wells in 1981 forvolatile organic compounds identified two with contaminants (13). One well had 25 ppb vinyl chloride, 15 ppb benzene, 28 ppbethylbenzene, and less than 10 ppb of chlorobenzene. The vinylchloride concentration was estimated and chlorobenzene waspresent but below the quantification limit of 10 ppb. The othercontaminated well had ethylbenzene present but below thequantification limit of 10 ppb. Both of those two contaminatedwells were dug rather than drilled.
|CONTAMINANT||MAXIMUM LEVEL IN PPB||COMPARISON VALUE2|
|methyl ethyl ketone||230||200ltha|
|methyl isobutyl ketone||360||none|
|1 -||The source of the data is the FS (6).|
|2 -||EMEGs are ATSDR's environmental media evaluation guides. CREGs are cancer risk evaluation guides and are calculatedfrom EPA's cancer slope factors. MCLs are EPA's maximumcontaminant levels. RfDs are EPA's Reference Doses. LTHAs are EPA's lifetime drinking water health advisories. AL is EPA's action level for lead in drinking water.|
|*||This chemical is considered a known human carcinogen.|
|**||This chemical is considered a probable human carcinogen.|
|***||This chemical is considered a known human carcinogen forthe inhalation route of exposure, but is not considered acarcinogen for ingestion.|
In this section of the public health assessment, the possibleexposure pathways are evaluated to help determine whether personshave, are, or will be exposed to contaminants associated with thesite. This pathway analysis consists of five elements (12):
|(1)||identifying contaminants of concern,|
|(2)||determining that these contaminants have/are/will betransported through an environmental medium,|
|(3)||identifying a point of exposure (i.e., a place orsituation where humans might be exposed to thecontaminated media),|
|(4)||determining that there is a plausible route of humanexposure (i.e., can the contaminant enter the body?), and|
|(5)||identifying an exposed population (i.e., how manypeople, if any, are at the point of exposure).|
An exposure pathway is considered complete when there is goodevidence that all five elements exist. The presence of acompleted pathway indicates that human exposure to contaminantshas occurred in the past, is currently occurring, or will occurin the future. When one or more of the five elements of anexposure pathway are missing, that pathway is consideredpotential. The presence of a potential exposure pathwayindicates the human exposure to contaminants could have occurredin the past, could be occurring now, or could occur in thefuture. An exposure pathway can be eliminated if at least one ofthe five elements is missing and will never be present.
A. Completed Exposure Pathway
Based on a review of the available data, past ingestion ofcontaminated groundwater is the only completed exposure pathway. Sampling done in 1981 identified two contaminated wells (13). One had 25 ppb vinyl chloride, 15 ppb benzene, less than 10 ppbchlorobenzene, and 28 ppb ethylbenzene. The other had less than10 ppb ethylbenzene. Use of those two wells reportedly ceasedshortly after the sampling was done (9). It is estimated thatthe maximum length of exposure for the users of those two wellswas eleven years (9). Additional residential wells in the areaaround Dover Landfill have also been reported to be contaminated(6,7). However, 21 residential wells around the site have beensampled periodically since 1985 with no contamination detected(6,7). The possible health implications of this completedexposure pathway will be evaluated in the ToxicologicalEvaluation section.
B. Potential Exposure Pathway
On-site soil, on- and off-site air, and off-site surface waterall represent potential exposure pathways. See the HumanExposure Pathways portion of the original public healthassessment for a discussion of those potential exposure pathways(9). There will be no further discussion of those potentialexposure pathways because the environmental data for thosepathways are limited, inappropriate for health evaluation, ornon-existent.
As discussed in the Pathways Analyses section, past ingestion ofcontaminated groundwater is the only completed exposure pathway. Exposure to 25 ppb vinyl chloride, 15 ppb benzene, less than 100ppb chlorobenzene, and 28 ppb ethylbenzene occurred in oneresidential well and to less than 10 ppb ethylbenzene in anotherwere identified in sampling done in 1981 (13). It is estimatedthat the maximum length of exposure for the users of those twowells was eleven years (9). On-site soil, on- and off-site air,and off-site surface water all represent potential exposurepathways, but will not be evaluated further as discussed in thepreceding section.
The Toxicological Evaluation portion of this section will discussthe possible health consequences from exposure to thecontaminants in the two private drinking water wells. Communityhealth concerns will be addressed in Community Health ConcernsEvaluation section and health outcome data in the Health OutcomeData Evaluation section.
Typically, the toxicological evaluation in a public healthassessment involves comparison of the exposure dose for thoseindividuals in an exposure pathway to ATSDR's Minimal Risk Levels(MRLs) or EPA's Reference Doses (Rfd). The MRLs and Rfds areestimates of daily human exposure to a contaminant below whichnoncarcinogenic adverse health effects are unlikely to occur(14). This means that any exposure dose that is below theappropriate MRL or Rfd, does not represent a hazard to humanhealth. The finding of an exposure dose above the appropriateMRL or Rfd indicates that evaluation of the toxicologicalliterature needs to be done to determine whether the specificexposure situation represents a hazard to public health. Theexposure dose, based on the contaminant concentrations andexposure length for the area where exposure has, is, or could occur, is compared to the MRL or Rfd appropriate for the route and length of exposure.
The risk of carcinogenic health effects is also evaluated in thissection. EPA's Cancer Slope Factor for a contaminant is used tocalculate the maximum risk from 70 years of exposure. The actualrisk of cancer is probably lower than the calculated number. The method used to calculate EPA's Cancer Slope Factor assumesthat high dose animal data can be used to estimate the risk forlow dose exposures in humans (15). The method also assumes thatthere is no safe level for exposure (16). There is littleexperimental evidence to confirm or refute those two assumptions. Lastly, the method computes the 95% upper bound for the risk,rather the average risk, which results in there being a 95%chance that the risk is actually lower, perhaps several orders ofmagnitude (17).
In this section, the exposure doses and carcinogenic risk will becalculated for the contaminants in the exposure pathway stillbeing considered. The possible health consequences of thosecontaminants which exceeded health guidelines will then bereviewed.
Calculation of Exposure Doses and Carcinogenic Risk
The exposure doses for ingestion of water were calculated in thefollowing manner. The maximum concentration for a contaminantwas multiplied by the water ingestion rate for adults of twoliters/day or for children, one liter/day. This product wasdivided by the average weight for an adult, 70 kg (154 pounds) orfor a child, 10 kg (22 pounds). A qualitative summary of theseresults can be found in Table 5. The maximum concentrations of chlorobenzene and ethylbenzene did not exceed the healthguideline for the chemical. There was no health guidelineavailable for the non-carcinogenic health effects of benzene. The maximum concentration of vinyl chloride from one well didexceed the health guideline for children and adults and will beevaluated further.
Carcinogenic risk from ingestion of water was calculated throughthe following. The maximum concentration of a contaminant wasmultiplied by the ingestion rate for adults of two liters/day,then this result is divided by the average adult body weight of70 kg. This product is multiplied by the EPA's Cancer SlopeFactor for the contaminant. This result represents the maximumrisk for cancer after 70 years of exposure. Because the maximumexposure appears to have only 11 years situation, the result wasmultiplied by 11/70 to adjust for this shorter exposure period.
The calculated maximum risk from ingestion of water contaminatedwith the maximum concentration of benzene does not represent anincreased risk of cancer. Because of this, carcinogenic healtheffects for this chemical will not be evaluated further. Acancer potency factor was not available for vinyl chloride, so itwas not possible to calculate the maximum excess cancer risk forthis chemical. Ethylbenzene and chlorobenzene have not beenclassified as to their ability to cause cancer.
|MRL||Minimal Risk Level established by the Agency for Toxic Substances and Disease Registry|
|RfD||Reference Dose established by the Environmental Protection Agency|
|mg/kg/day||milligrams of chemical per kilogram of body weight per day|
Possible Health Consequences
The possible health consequences of vinyl chloride is describedin the following paragraphs.
Vinyl chloride is a colorless vapor with a mild sweet odor (18). It can exist in liquid form if it is kept under high pressure. Almost all vinyl chloride is man-made. Most of the vinylchloride produced in the United States is used to make polyvinylchloride (PVC). PVC is used to make a variety of plasticproducts including pipes, wire and cable coatings, and packingmaterials. Other uses include furniture and automobileupholstery, wall coverings, housewares, and automotive parts. Atone time, vinyl chloride also was used as a coolant, a propellantin spray cans, and in some cosmetics. It is no longer used forthese purposes.
There are a number of reports in the literature on the healthfrom exposure of humans to vinyl chloride via the inhalationroute of exposure, but none for the ingestion route (18). Therefore, information from animal studies will be used toevaluate the possibility of health effects.
There is some chance that long-term exposure to vinyl chloride atthe concentration identified in the Dover Landfill area, 25 ppb,could result in mild health effects to the liver, but not toother organ systems (18). This conclusion is based on a study ofrats exposed to vinyl chloride in feed for 149 weeks (18). Therewas an increase in the incidence of basophilic nuclei in livertissue at a dose of 0.018 mg/kg/day. This dose is 7.2 timesgreater the exposure dose for children and 25 times greater thanfor adults. While the exposure doses are lower, it cannot bestated with any certainty that adverse health effects could notoccur. There is always uncertainty when using animal studies toevaluate the possibility of adverse human health effects. Thereis also uncertainty because of the possible variability betweenindividuals in response to exposure. In addition, there isuncertainty about the specific length and level of exposure tovinyl chloride at the one well in the Dover Landfill where it wasidentified.
The latest available data from the New Hampshire State CancerRegistry indicated that there is no known increase in the cancerincidence rate for the City of Dover, NH at this point in time (10).
EPA's response to the concern about future contamination of theBellamy Reservoir was that the proposed leachate collection ditcharound the landfill should intercept most of the leachate whichmight potentially migrate off-site. It is not thought thatcontaminants from the site would reach the reservoir at levels ofhealth concern with the implementation of the proposed cleanupplan for the site.
The other health-related concern was the possible consequences tochildren who used the bus stop near the discharge point of aculvert which runs from an on-site area to an off-site stream. EPA conducted eight hour sampling of the air at two locationsnear the bus stop (6). The levels found do not represent a health hazard for individuals exposed for the relatively fewminutes one would be at a bus stop. However, one day of the airsampling cannot predict what the typical exposure might havebeen, so further evaluation of this concern is not possible.