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This health consultation evaluates the potential health impact associated with exposure to landfill gases(particularly hydrogen sulfide and volatile organic compounds) that are being released from the FourHills Landfill in Nashua, New Hampshire while this facility is being closed out. This report has beenprepared in response to local residents' health concerns about exposure to these gases. This documentwas prepared by the New Hampshire Bureau of Environmental and Occupational Health (BEOH) throughits cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR).

Site Description and History:

The Four Hills Landfill site covers 300 acres in the southwestern section of Nashua, New Hampshire. Nashua is New Hampshire's second most populous urban area, and there are many residentialneighborhoods relatively close to the site. Landfill operations began at Four Hills in 1971. Today, manysections of the site have been capped and are no longer in use, but several other waste managementactivities continue at Four Hills. These operations include: a solid waste bailing facility, a landfill gas-to-energy facility, recycling facilities, and a yard waste compactor [DES 1999]. The active landfill operationat Four Hills accepts residential and commercial waste generated in the City of Nashua [City of Nashua2002]. The landfill does not accept hazardous waste, anti-freeze, or gasoline.

In past years, residents of neighborhoods surrounding the Four Hills landfill complained of odors andraised concerns regarding possible health effects associated with chemicals released from the site. Thenumber of complaints has dropped significantly after improved gas collection, capping, groundwater protection, and other major projects were completed at the site during the late 1990s [DES 1999]. InAugust 2002, an inquiry from a Nashua resident was referred to BEOH by the New HampshireDepartment of Environmental Services (DES). Many residents had concerns the health effects of inhalinglandfill gas. One citizen inquiry was concerned about the developmental effects of exposure to landfillgas during pregnancy. Inhalation of landfill gas the primary subject of investigation discussed in thishealth consultation.

Overview of Sampling Data:

The City of Nashua and DES conducted weekly monitoring of landfill gasses at the ground surface aswell as around wellheads and piping [DES 1999]. These on-site monitoring activities are important, butare not reliable for predicting off-site ambient air concentrations of landfill gases. Actual ambient airmonitoring data for neighborhoods surrounding Four Hills is very limited. Relevant data that have beenprovided to BEOH are shown here as Table 1.

Off-site monitoring took place in three locations: Main Dunstable School, Aster Court (in the Ledgewoodarea) and at the entrance to the landfill on West Hollis Street. Analysis was completed for volatileorganic compounds (VOCs) and reduced sulfur compounds (which includes hydrogen sulfide). Samples were collected in March 1999 and March 2000.


Chemicals of Concern

The major chemicals of concern in landfill gas exposures and odor complaints are VOCs and reducedsulfur compounds.

Pathway for Exposure to Site Contamination:

The exposure pathway of concern for people living near the Four Hills Landfill site is inhalation oflandfill gas containing reduced sulfur compounds and VOCs.

Hydrogen Sulfide

There are numerous compounds associated with the decay of organic matter. A small fraction of thesecompounds, known as the reduced sulfur compounds, are of interest since they are toxicologicallysignificant in terms of inhalation exposure to landfill gas [ATSDR 2002].

Hydrogen sulfide is a colorless gas [ATSDR 1999a; IDPH 2002] with a strong odor of rotten eggs. Among the sulfide compounds, hydrogen sulfide is emitted from landfills at the highest rates andconcentrations [ATSDR 2002]. Hydrogen sulfide can be released from oil refineries and natural gasproduction facilities. It also is formed naturally when bacteria break down sulfur-containing organicmatter. Hydrogen sulfide is released from sewage and animal wastes, and is commonly known as "sewergas". Organic wastes in landfills are another common source of hydrogen sulfide gas [ATSDR 1999a;IDPH 2002].

Among the air samples that were taken in residential areas near the Four Hills site, concentrations of 51 and 57 µg/m3 (approximately 37 and 41 ppb) were recorded [Cambridge 2000]. The other samples were below the detection limit of 35 µg/m3 (approximately 25 ppb) [Cambridge 2000]. The ATSDR Minimal Risk Level (MRL) for residential inhalation exposures to hydrogen sulfide from hazardous waste sites is 30 parts per billion (approximately 41.8 µg/m3).


VOCs are another class of chemicals that are commonly a bi-product of landfills. They also are known toproduce odors even though they are emitted at trace (very low) concentrations. Toluene and xylene (bothm,p-xylene and o-xylene) were the compounds measured in the ambient air near the Four Hills landfill. They have aromatic odors similar to benzene. These VOCs come from solvent-containing materials thatwere commonly dumped into older, unregulated landfills.

The applicable comparison value for chronic inhalation exposures to toluene is approximately 301 µg/m3 (approximately 80 ppb). The applicable comparison value for residential inhalation exposures to total xylenes is approximately 1,303 µg/m3 (approximately 100 ppb).

Recorded levels of total xylenes (m,p- and o-xylene) and toluene were far below (in the case of xylene,several orders of magnitude) their respective health comparison values (see table). Even though few airsamples were taken, it is unlikely that these VOCs could reach hazardous levels. Therefore, adversehealth effects from exposure to these levels of total VOCs are not expected.

Public Health Implications of Exposures to Site Contamination:

Hydrogen Sulfide

The two samples that did indicate hydrogen sulfide levels above the comparison value are well below the documented levels at which adverse health effects are known to occur. The applicable comparison value (30 ppb or approximately 41.8 µg/m3) was derived from a study in rats in which health effects were actually seen at 30,500 ppm (approximately 42,500 µg/m3). This difference between the effect seen in the study and the actual comparison value adjust for uncertainty in extrapolating animal data to be used to protect human populations. The comparison value is designed to be conservative, therefore actual health effects may not occur unless a much higher exposure takes place.

The strong "rotten egg" odor of hydrogen sulfide is noticeable to most people at air concentrations at orabove 0.5 ppb [ATSDR 1999a]. At higher concentrations, however, the human sense of smell canbecome insensitive to the odor of hydrogen sulfide. This desensitization occurs when concentrationsreach 50,000 to 100,000 ppb [IDPH 2002]. Therefore, one's sense of smell is not always a reliableindicator of the presence of hydrogen sulfide gas.

Health effects of short-term exposures will usually subside within a few weeks after exposure has ceased[ATSDR 1999a; IDPH 2002]. Longer-term, lower level inhalation exposures can result in fatigue, loss ofappetite, headaches, irritability, poor memory, dizziness as well as respiratory symptoms such as nasalproblems [ATSDR 1999a]. Hydrogen sulfide has not been shown to cause cancer in humans, and has notbeen classified as a carcinogenic substance by the United States Environmental Protection Agency[USEPA 2002] or by the International Agency for Research on Cancer [IARC 2002].

Independent studies have shown that hydrogen sulfide exposures are related to some types of healthproblems in humans. In a controlled laboratory study by Jappinen et al. [1990], human subjects exposedto 10,000 ppb hydrogen sulfide always reported an unpleasant odor and sometimes experiencedheadaches. Rossi et al. [1993] found that there was a statistical association with emergency roomattendances for asthma attacks and weekly mean concentrations of hydrogen sulfide concentrations up to10,000 ppb.

As well, some ATSDR studies of residential communities indicate that hydrogen sulfide may be related toadverse health effects. In 1999, ATSDR conducted a health study of communities near the Fresh KillsMunicipal Landfill in Staten Island, New York. ATSDR focused on asthma, and how factors such ashydrogen sulfide concentrations and proximity of residence to the landfill affected respiratory function. A group of 148 community residents with asthma volunteered to participate in the study. For a 6-weekperiod in summer 1997, study participants completed a daily diary to record perceived odors, respiratorysymptoms and daily activities. Participants also measured their lung function each morning and evening. During this same period, ATSDR conducted continuous monitoring in the study area to assess ambient airconcentrations of hydrogen sulfide, as well as other factors that can trigger asthma. They discovered thatwhen study participants reported that they smelled rotten eggs or garbage, they also reported that theywere more likely to wheeze or experience difficulties in breathing. A moderate decline in lung functionwas also documented when participants reported these odors [ATSDR 1999b].

In another study, ATSDR investigated levels of reduced sulfur compounds and respiratory- and digestive-related hospitalization rates in Nebraska. For adults, a positive association was found between hospitalvisits for respiratory diseases and the reduced sulfur compound levels of the previous day. For children, apositive association between hospital visits for respiratory diseases and the reduced sulfur compoundlevels as well as hydrogen sulfide levels of the previous day. No associations were found betweenreduced sulfur compound levels and hospital visits for digestive diseases [ATSDR 1997].

Regarding hydrogen sulfide exposures and developmental effects of the fetus, study results are inconsistent as to whether or not there is an association. Hemminki and Niemi [1982] analyzed pregnancy complications in an industrial community in Finland, finding an increased rate of spontaneous abortion in all socioeconomic classes in areas where the mean annual level of hydrogen sulfide exceeded 4 µg/m3. However, limited data in this study prevented the authors from drawing statistically useful conclusions from their results. In another study by Fielder et al. [2000], rates of stillbirths, spontaneous abortions and birth defects were examined in community near a landfill in Wales, England. There was no difference between the rate of these pregnancy complications from before and after the opening of the landfill. Only one available study, by Xu et al. [1998], did show a statistical link between pregnancy complications and hydrogen sulfide exposure. This study showed that female petrochemical employees in China experienced statistically higher rates of spontaneous abortion than did female workers from non-chemical plants. Although this study is important, it may represent an exposure that is much higher than would be expected at non-occupational levels and may involve many other chemicals.

In regards to hydrogen sulfide, the number of ambient air samples taken in residential areas near the FourHills site is too small to provide a representative picture of what residents are/were exposed to on a day-to-day basis. Furthermore, the report [Cambridge 2000] from which these data were drawn did not discussweather conditions or site activities/conditions at the time the samples were gathered, which further limitsour ability to provide definitive conclusions from these data. Additionally, the hydrogen sulfide detectionlimit (35 µg/m3) precludes further characterization at two sampling sites (Astor Court and DunstableSchool). In light of these limitations, DHHS cannot conclusively determine whether residents within thevicinity of the former Four Hills Landfill were exposed to harmful concentrations of hydrogen sulfide in the past, nor can current or future exposure conditions be accurately assessed.


Children are at a greater risk than adults from certain kinds of exposure to hazardous substances emittedfrom waste sites. They are more likely to be exposed for several reasons (e.g., they play outdoors moreoften than adults, increasing the likelihood that they will come into contact with chemicals in theenvironment). Because of their smaller stature, they may breathe dust, soil, and heavy vapors close to theground. Children are also smaller, resulting in higher doses of chemical exposure per body weight. Thedeveloping body systems of children can sustain permanent damage if certain toxic exposures occurduring critical growth stages. Most importantly, children depend completely on adults for riskidentification and management decisions, housing decisions, and access to medical care.

Children are likely to be exposed to hydrogen sulfide in the same manner as adults with the exception ofadults at work. However, because hydrogen sulfide is heavier than air and because children are shorterthan adults, children may be exposed to larger amounts of hydrogen sulfide than adults [ATSDR 1999a].


  1. Levels of toluene and total xylenes appear to be well below their respective comparison values. Even with current ambient air monitoring data, it is unlikely that these chemicals will be found abovetheir comparison values. Therefore, BEOH considers exposures to toluene and total xylene emissionsfrom the Four Hills Landfill site to be no apparent public health hazard.

  2. Adequate ambient air monitoring data for hydrogen sulfide are not available. BEOH is unable toassess past, present or future health risks. Therefore, BEOH considers exposures to hydrogen sulfideemissions from the Four Hills Landfill site to be an indeterminate public health hazard.

  3. Studies by ATSDR and others demonstrate that respiratory problems can occur in populationsexposed to hydrogen sulfide. In regards to pregnancy effects, study results are inconsistent as towhether or not there is a relationship between exposure and adverse birth effects. Therefore, wecannot determine with any degree of certainty whether the exposures at the site are related toadverse pregnancy outcomes.


  1. Ambient air monitoring of the area around the Four Hills Landfill should continue.

  2. In addition to ambient air monitoring, screening level air monitoring should be considered tosupplement monitoring data. Screening level air modeling is a computer simulation in which conditionsare presumed to be the highest typical exposure scenario (e.g., typical average summer conditions with relatively high temperatures and humidity and little or no wind speed).

  3. Area residents experiencing pregnancy complications or other health problems should seekappropriate medical treatment, regardless of whether those health effects are attributable to inhalation of hydrogen sulfide gas.

  4. Future sampling should take place during the summer. High temperatures and high humidity are optimal conditions for fugitive landfill gas emissions.

  5. If future ambient air quality monitoring is conducted, sampling procedures with lower detectionlimits should be used. Current sampling techniques have detection limits as low as 4 µg/m3.


The purpose of the Public Health Action Plan is to ensure that this document not only identifies anycurrent or potential exposure pathways or related health hazards, but also provides a plan of action tomitigate and prevent adverse human health effects resulting from exposures to hazardous substances inthe environment. The first section of the Public Health Action Plan contains a description of completedor ongoing actions to mitigate exposures to environmental contamination. In the second section, there is a list of additional public health actions that will be implemented in the future.

Completed or Ongoing Actions:

  1. A landfill gas collection/treatment system was installed in the mid 1990s. The capacity and efficiency of this system were greatly increased during 1999.

  2. City of Nashua and DES personnel conduct periodic inspections of capped areas of the site, as well as piping, wellheads, etc. Weekly measurements are collected of gas released at the ground surface, and around wellheads, piping, etc.

  3. Several sections of the site have been capped with low-permeability soil, to minimize gas leakage and rainwater penetration. Most capping was completed by mid-1999.

Planned Actions:

  • DHHS will review new data for the site and provide health advice to DES when necessary.


Samuel C. Yamin, MPH
Environmental Toxicologist
Todd C. Hudson, MSPH
Environmental Health Risk Analyst

Bureau of Environmental and Occupational Health
New Hampshire Department of Health and Human Services
Concord, New Hampshire
(603) 271-4664
(603) 271-3991 (fax)

Table 1.

Ambient Air Concentrations Chemicals of Interest [from Cambridge 2000]
Ambient Air Concentrations, µg/m3
March 1999 March 2000
Residence, West Hollis Street Main Dunstable School Residence, Conant Street Astor Court Main Dunstable School Landfill Entrance, W. Hollis Street Comparison Value
Hydrogen Sulfide ND (35) 51 57 ND (35) ND (35) ND (35) 41.8 (MRL)
m,p-Xylene 2.4 7.5 3.6 ND (2.2) ND (2.2) NA 1,303 (MRL)
o-Xylene ND (2.2) 3.7 ND (2.2) ND (2.2) ND (2.2) NA 1,303 (MRL)
Toluene ND (2.2) 87 ND (2.2) ND (2.2) ND (2.2) NA 301 (MRL)

ND indicates that compound was not detected--lower detection limit is in parentheses.
MRLs were converted from parts per billion (ppb) standards, assuming normal temperature and pressure.


The Health Consultation on the Four Hills Landfill Site, Nashua, New Hampshire was prepared by the New Hampshire Department of Health and Human Services 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.

Gregory V. Ulirsch, M.S.
Technical Project Officer
Superfund Site Assessment Branch (SSAB)
Division of Health Assessment and Consultation (DHAC)

The Division of Health Assessment and Consultation, ATSDR, has reviewed this Health Consultation and concurs with its findings.

Roberta Erlwein


Agency for Toxic Substances and Disease Registry (ATSDR). 1997. Exposure Investigation: HydrogenSulfide in Ambient Air; Dakota City/South Sioux City, Nebraska. Atlanta: U.S. Department of Health andHuman Services.

Agency for Toxic Substances and Disease Registry (ATSDR). 1999a. Toxicological Profile for HydrogenSulfide. Atlanta: U.S. Department of Health and Human Services.

Agency for Toxic Substances and Disease Registry (ATSDR). 1999b. A Panel Study of Acute RespiratoryOutcomes, Staten Island, New York. Draft Final Report for Public Comment. Atlanta: U.S. Department ofHealth and Human Services.

Agency for Toxic Substances and Disease Registry. 2002. Landfill Gas Primer. Atlanta: U.S. Departmentof Health and Human Services.

Cambridge Environmental Inc. 2000. Evaluation of Risks to Human Health Potentially Associated with theEmission of Landfill Gas from the Four Hills Landfill, Nashua, New Hampshire.

City of Nashua, New Hampshire, Division of Public Works, Solid Waste Department. 2002. Four Hills Landfill. .

Fielder, H. M., C. M. Poon-King, et al. 2000. Assessment of impact on health of residents living near theNant-y-Gwyddon landfill site: retrospective analysis.comment. Brit Med J 320(7226): 19-22.

Hemminki K, Niemi ML. 1982. Community Study of Spontaneous Abortions: Relation to Occupation and AirPollution by Sulfur Dioxide, Hydrogen Sulfide, and Carbon Disulfide. Int Arch Occ Env Health 51(1): 55-63.

Illinois Department of Public Health, Division of Environmental Health. 2002. Fact Sheet: Hydrogen Sulfide Gas. .

Jaakkola JJK, Paunio M, Virtanen M, et al (1991). Low-level air pollution and upper respiratory infections in olderchildren. Am J Public Health 81:1060-1063.

Jappien P, Vikki V, Marttila O, et al. 1990. Exposure to hydrogen sulfide and respiratory function. British J ofIndust Med 47: 824-828.

New Hampshire Department of Environmental Services (DES). 1999. Nashua Four Hills Landfill: On-going Improvements for Odor Control. Concord, New Hampshire.

Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

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