PUBLIC HEALTH ASSESSMENT
PALM CITY, MARTIN COUNTY, FLORIDA
ATSDR evaluates contaminants detected in environmental media at the site and determines whether an exposure to them has public health significance. Please refer to Appendix D for information on health-based comparison values and Appendix E for information on ATSDR's methodology. For this public health assessment, ATSDR staff obtained and evaluated environmental data for groundwater, soil, and sediment.
- Groundwater, On-Site Sampling Events
Several on-site groundwater sampling events occurred between 1992 and 1998. In January 1992, on-site groundwater sampling was conducted from temporary well number 1 and temporary well number 2 (McGinnes Laboratories, 1992). Samples were tested for organophospate pesticides and polychlorinated biphenyls (PCBs). In October 1995 and February 1996, samples were again collected and tested for pesticides and PCBs from on-site wells (ATSDR, 1996a; Evergreen Engineering, 1996). Historical sampling results were compiled by Evergreen Engineering for the Florida Department of Environmental Protection (Evergreen Engineering, 1996).
Chlordane was the only contaminant detected in the temporary wells more than one time, in the past, at levels above ATSDR comparison values. Benzene; beta BHC; 4,4' - DDD; 4,4' - DDE; and diazinon were all detected in one location at levels above ATSDR comparison values. Please refer to Table 3, Appendix C, for the results of these groundwater sampling events.
In a review of site file information, ATSDR obtained a letter indicating that Dupont had sampled an irrigation well (FDEP, 1995). Unfortunately, ATSDR was not able to find any other information on this irrigation well, including the sampling data.
In March 1998, the EPA and FDEP collected groundwater samples from three temporary on-site wells (EPA, 1998c). Please refer to Figure 1, Appendix B, for the sampling locations. The samples were analyzed for metals, volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), and pesticides. The samples were also analyzed for benlate as carbendazim. The benlate is converted to carbendazim in the laboratory analysis procedure, so this procedure measures both benlate and carbendazim in the sample (ATSDR, 1998d). During this March 1998 sampling event, only arsenic was detected at a level that was above ATSDR comparison values in one location. The EPA data indicated that carbendazim was not detected. Please refer to Table 3, Appendix C, for the results of this on site groundwater sampling event.
Samples were also collected from the one on-site private well in August 1993 and March 1998. In 1993, the sample was analyzed for VOCs and SVOCs (HRS, 1996b). In March 1998, the sample was analyzed for metals, VOCs, SVOCs, pesticides, and carbendazim. No VOCs, SVOCs, or pesticides were detected. The EPA data indicated that carbendazim was also not detected. However, several metals were detected. The sampling data for this private well are included in Table 4, Appendix C.
- Groundwater, Off-site Sampling Events
During the period from 1993 to December 1996, the Martin County Health Department tested 36 private wells around the Loxahatchee Nursery site (EPA, 1998a). The samples were analyzed for VOCs, SVOCs, and pesticides (HRS, 1996b). In July 1996, the contaminant 1,2-dichloropropane was detected at a maximum level of 150 ppb in a private well. This private well was fitted with a carbon filter in August 1996 which removes the contaminant from the water (EPA, 1998a).
The private well that contained elevated levels of 1,2-dichloropropane in July 1996 was retested on several occasions. This private well contained 1,2-dichloropropane at a maximum level of 330 ppb in November 1996. Of note, the November 1996 sample was collected from raw, unfiltered water (ATSDR, 1998c). These levels of 1,2-dichloropropane are above EPA's MCL of 5 ppb, but below ATSDR's chronic child EMEG of 900 ppb. In addition, three VOCs (bromodichloromethane, chloroform, and dibromochloromethane) were detected in this same private well in raw, unfiltered water at levels above ATSDR cancer risk evaluation guides (CREGs); however, all three chemicals were below detection limits after treatment from the carbon filter.
In March 1998, the EPA and FDEP collected groundwater samples from four off site private wells (EPA, 1998c). One off site temporary well was also sampled as a part of this sampling event. This temporary well, TW01, was sampled to establish background conditions; however, for the purpose of this public health assessment, ATSDR did not consider the sampling results from this well as indicative of background conditions of the area groundwater. ATSDR's rationale for this decision is based on the location of the well (just across the street from the site) and the Agency's inability to obtain any documentation indicating that groundwater flow beneath the site is not toward this well.
The March 1998 samples were analyzed for metals, VOCs, SVOCs, pesticides, and carbendazim. Arsenic was detected in the temporary well (TW01) above ATSDR comparison values. Arsenic was not detected in any private wells. The EPA data indicated that carbendazim was not detected in private or temporary monitoring wells. Please refer to Table 4, Appendix C, for the results of the March 1998 sampling event.
- Soil, On-Site Sampling Events
Several on-site soil sampling events have occurred between 1992 and 1998. In January 1992, two on-site soil samples were collected from an unspecified depth (Evergreen Engineering, 1996). In April 1992, a sample was collected from the soil stockpile at an unspecified depth (Evergreen Engineering, 1996). In February 1996, four soil samples within, and adjacent to, the soil stockpile were collected from an unspecified depth (ATSDR, 1996a). For the previously described sampling events, all the samples were tested for pesticides and PCBs. Chlordane was detected in all of the samples. Please refer to Table 5, Appendix C, for the results of the 1992 and 1996 on-site soil sampling events.
In March 1998, the EPA and FDEP sampled on-site soils throughout the nursery site to determine the presence or absence of contamination. The samples were analyzed for metals, VOCs, SVOCs, pesticides, and carbendazim. At each sampling location, two depths intervals were collected. One surface soil sample was collected from a depth of 0-3 inches below land surface (bls) except for the portion for volatile analysis, which was collected at a depth of 6-12 inches bls (EPA, 1998c). A second sample at each location was collected from a depth of 1.0-1.5 feet bls (ABB-ES, 1998). Soil samples were also obtained from the two depth intervals from the yard of the on-site residence (SS05). Please refer to Figure 1, Appendix B, for the sampling locations. Deep subsurface soil samples were not collected as initially proposed in the work plan because of the shallow depth-to-groundwater at the site, which is approximately 1.5-2.0 feet bls (ABB-ES, 1998). The groundwater table in this area fluctuates depending on the season.
No contaminants from the on-site residence exceeded ATSDR comparison values. Gamma chlordane in sample SS03A, cadmium in sample SS10A, and benzo(a)pyrene in sample SS09A exceeded ATSDR comparison values on the nursery property. Arsenic, chromium, manganese, and chlordane exceeded ATSDR comparison values on the nursery property in several sampling locations. The EPA data indicated that carbendazim was not detected. Please refer to Table 6, Appendix C, for the results of this on-site surface soil sampling event.
- Soil, Off-Site Sampling Events
In March 1998, the EPA and FDEP sampled off-site soils at two locations. One location (SS08) was sampled to determine the presence or absence of contamination. The other location (SS01) was sampled to establish background conditions; however, for the purpose of this public health assessment, ATSDR did not consider the sampling results from SS01 as indicative of background conditions. ATSDR's rationale for this decision is based on the location of the sample (just across the street from the site) and the agency's inability to obtain any documentation indicating that this area has not been impacted by site activities.
The samples were analyzed for metals, VOCs, SVOCs, pesticides, and carbendazim. At each sampling location, two depths intervals were collected. One surface soil sample was collected from a depth of 0-3 inches bls, except for the portion for volatile analysis which was collected at a depth of 6-12 inches bls (EPA, 1998c). A second sample at each location was collected from a depth of 1.0-1.5 feet bls (ABB-ES, 1998). Please refer to Figure 1, Appendix B, for the sampling locations labeled as SS01 and SS08. Subsurface soil samples were not collected as initially proposed in the work plan because of the shallow depth-to-groundwater at the site, which is approximately 1.5-2.0 feet bls (ABB-ES, 1998). Arsenic, chromium, and manganese exceeded ATSDR comparison values. The EPA data indicated that carbendazim was not detected. Please refer to Table 7, Appendix C, for the results of this off-site surface soil sampling event.
- Sediment Sampling Events
For the March 1998 sampling event, the EPA and FDEP had planned to collect a sediment sample from the on-site ponds to determine the presence or absence of contamination. However, a sample could not be obtained from the smaller pond because it had been filled in. The site team attempted to sample the sediment from the second pond, but could not obtain a representative sample with the standard sampling equipment (ABB-ES, 1998; ATSDR, 1998e).
During this March 1998 sampling event, the EPA and FDEP were able to collect sediment samples from the shallow drainage ditches bordering the site, as well as from the South Fork of the St. Lucie River. One sediment location (SD01) was sampled to establish background conditions; however, for the purpose of this public health assessment, ATSDR did not consider the sampling results from SD01 as indicative of background conditions. ATSDR's rationale for this decision is based on the location of the sample (just across the street from the site) and the agency's inability to obtain any documentation indicating that this area has not been impacted by site activities.
The samples were analyzed for metals, VOCs, SVOCs, pesticides, and carbendazim. The sediment samples were collected below water (EPA, 1998c). Manganese was detected above comparison values in the drainage ditches and the South Fork of the St. Lucie River sample. Arsenic, chromium and vanadium exceeded ATSDR comparison values only in the drainage ditches. The EPA data indicated that carbendazim was not detected. Please refer to Table 8, Appendix C, for the results of this sediment sampling event.
- Water, On-Site Tank Pull Sampling Event
During removal of an abandoned underground storage tank in 1992, water samples were collected from the bottom of the tank (ATSDR, 1996a). The water samples were analyzed for pesticides and gasoline constituents. Several contaminants exceeded ATSDR drinking water comparison values; however, this water from the underground tank was not used as a drinking water source. Please refer to Table 9, Appendix C, for the results of this sampling event.
The Loxahatchee Nursery site is not currently fenced. Therefore, community members, including
children, have unlimited access. During ATSDR's site visit, the staff noted that most of the site
was overgrown with tall weeds, and the on-site pond was not viewable from the nursery's dirt
road. The remaining structures on site were in a state of disrepair, and there was evidence of
trespassing (i.e., graffiti on the structures); therefore, ATSDR concludes that the on-site ponds
and dilapidated structures pose a potential physical hazard to area residents, especially children, who trespass on site.
To determine whether people were, or continue to be, exposed to contaminants originating from Loxahatchee Nursery site, ATSDR evaluated the factors that lead to human exposure. These factors, or elements, include (1) a source of contamination, (2) transport through an environmental medium, (3) a point of exposure, (4) a route of human exposure, and (5) an exposed population. Exposure pathways fall into one of three categories:
- Completed Exposure Pathway. ATSDR calls a pathway "complete" if it is certain that people are exposed to contaminated media. Completed pathways require that the five elements exist and indicate that exposure to the contaminant has occurred, is occurring, or will occur.
- Potential Exposure Pathway. Potential pathways are those in which at least one of the five elements is missing but could exist. Potential pathways indicate that exposure to a contaminant could have occurred, could be occurring, or could occur in the future. Potential exposure pathways refer to those pathways where (1) exposure is documented, but there is not enough information available to determine whether the environmental medium is contaminated, or (2) an environmental medium has been documented as contaminated, but it is unknown whether people have been, or may be, exposed to the medium.
- Eliminated Exposure Pathway. In an eliminated exposure pathway, at least one of the five elements is missing and will never be present. From a human health perspective, pathways can be eliminated from further consideration if ATSDR is able to show that (1) an environmental medium is not contaminated, or (2) no one is exposed to contaminated media.
ATSDR has identified a completed exposure pathway to off-site groundwater through private wells surrounding the nursery site. ATSDR has determined the exposures to on- and off-site soil, and on- and off-site sediment constitute potential exposure pathways. The specific elements associated with the completed exposure pathway and each potential exposure pathway are summarized in Table 1 and Table 2 (Appendix C), respectively. The following text also describes both the completed and potential exposure pathways identified for this site.
The residential homes surrounding the Loxahatchee Nursery site use private well water. Samples were collected and analyzed from nearby private wells from 1992 to 1998, and the contaminant 1,2-dichloropropane was detected in a private well at levels above the EPA's MCL. This private well is currently using a carbon filter which removes the contaminant from the water. Past, current, and future exposures exist from drinking, bathing, and irrigating with private well water. The routes of exposure include ingestion, inhalation, and dermal contact.
One residence is located on the nursery site. Adults and children living at this residence, as well as other nearby adults and children trespassing on the nursery site, may come into contact with on-site surface soil. When the nursery site was operational, pesticides and other chemicals were used. No contaminants were detected at levels exceeding ATSDR comparison values from the on-site residence. Gamma chlordane, chlordane, benzo(a)pyrene, arsenic, cadmium, chromium, and manganese were detected on the nursery property at levels exceeding ATSDR comparison values. Of note, cadmium, benzo(a)pyrene, and gamma chlordane were each detected above comparison values in only one sample of on-site soil. On-site residents and trespassers may have been, and may continue to be, exposed to on-site surface soil.
Nursery soil may have blown to off-site locations, or been carried to off-site locations, during flood events. Routes of potential exposure include dermal contact and incidental ingestion of off-site surface soil. While no VOCs, SVOCs, or pesticides were detected at levels exceeding ATSDR comparison values, three metals (arsenic, chromium, and manganese) were detected at levels that exceeded ATSDR comparison values. Of note, only two samples were collected from off-site locations by the EPA and FDEP in March 1998, and the levels detected may not be indicative of the levels of contaminants in soil throughout the surrounding residential area.
In March 1998, the EPA and FDEP collected sediment samples from the drainage ditches bordering the nursery site, as well as from the South Fork of the St. Lucie River. On-site pond sediment has not been characterized. Several metals (arsenic, chromium, manganese and vanadium) were detected above ATSDR comparison values in the drainage ditches and one metal (manganese) was detected above ATSDR comparison values in the South Fork of the St. Lucie River sediment sample. Children might play in the on-site pond and drainage ditches bordering the site, and individuals who use the South Fork of the St. Lucie River for recreational activities, including boating and swimming, might come into contact with sediment. Exposures to contaminants in sediment could occur during these activities, and both direct skin contact and incidental ingestion could be routes of exposure.
In this section, ATSDR addresses the likelihood that exposure to contaminants at the maximum concentrations detected would result in adverse health effects. While the relative toxicity of a chemical is important, the response of the human body to a chemical exposure is determined by several additional factors, including the concentration (how much); the duration of exposure (how long); and the route of exposure (breathing, eating, drinking, or skin contact). Lifestyle factors (i.e., occupation and personal habits) have a major impact on the likelihood, magnitude, and duration of exposure. Individual characteristics such as age, sex, nutritional status, overall health, and genetic constitution affect how a human body absorbs, distributes, metabolizes, and eliminates a contaminant. A unique combination of all these factors will determine the individual's physiologic response to a chemical contaminant and any adverse health effects the individual may suffer as a result of the chemical exposure.
ATSDR has determined levels of chemicals that can reasonably (and conservatively) be regarded as harmless, based on the scientific data the agency has collected in its toxicological profiles. The resulting comparison values and health guidelines, which include ample safety factors to ensure protection of sensitive populations, are used to screen contaminant concentrations at a site and to select substances ("chemicals of concern") that warrant closer scrutiny by agency health assessors and toxicologists.
It is a point of key importance that ATSDR's (and EPA's) comparison values and health guidelines represent conservative levels of safety and not thresholds of toxicity. Thus, although concentrations at or below a comparison value may reasonably be considered safe, it does not automatically follow that any concentration above a comparison value will necessarily produce toxic effects. To the contrary, ATSDR's (and EPA's) comparison values are intentionally designed to be much lower, usually by orders of magnitude, than the corresponding no-effect levels (or lowest-effect levels) determined in laboratory studies. ATSDR uses comparison values (regardless of source) solely for the purpose of screening individual contaminants. In this highly conservative procedure, ATSDR considers that a compound warrants further evaluation if the highest single recorded concentration of that contaminant in the medium in question exceeds that compound's lowest available comparison value (e.g., cancer risk evaluation guides or other chronic exposure values) for the most sensitive, potentially exposed individuals (e.g., children or pica children). This highly conservative process results in the selection of many contaminants as "chemicals of concern" that will not, upon closer scrutiny, be judged to pose any hazard to human health. However, ATSDR judges it prudent to use a screen that "lets through" many harmless contaminants rather than one that overlooks even a single potential hazard to public health. Even those contaminants of concern that are ultimately labeled in the toxicologic evaluation as potential public health hazards are so identified solely on the basis of the maximum concentration detected. The reader should keep in mind the protectiveness of this approach when considering the potential health implications of ATSDRs toxicologic evaluations.
Because a contaminant must first enter the body before it can produce any effect, adverse or otherwise, on the body, the toxicologic evaluation in public health assessments focuses primarily on completed pathways of exposure, i.e., contaminants in media to which people are known, or are reasonably expected to have been exposed, such as water that may be used for drinking water and air in the breathing zone.
A completed exposure pathway to groundwater was identified in one private well. ATSDR evaluated whether exposures to this private well water would pose a public health hazard. While this toxicologic evaluation section focuses primarily on groundwater contaminants, the contaminants in soil and sediment are also discussed.
Contaminants in Private Well Water
Exposure to private well water represents the only completed pathway identified at this site--the only pathway by which exposure to contaminants is known, or may be reasonably expected to be occurring, or have occurred. The maximum detected concentration of 1,2-dichloropropane (330 ppb) in one well did exceed EPA's MCL of 5 ppb by a substantial margin, but it was well below ATSDR's chronic child environmental media evaluation guide (EMEG). Based on the best medical and toxicological data available, ATSDR concludes that exposures to the levels of 1,2-dichloropropane detected in private well water pose no hazard to public health (ATSDR, 1989).
The apparent discrepancy between ATSDR and EPA comparison values is due to the fact that EPA still classifies 1,2-dichloropropane as a B2 carcinogen, based on its judgement that a rodent bioassay conducted by the National Toxicology Program (NTP) provided "sufficient" evidence of carcinogenicity in animals. (No such data exists for humans.) EPA policy requires that the MCL for all class A and class B carcinogens be as close to zero as is technically feasible, which explains why the MCL for 1,2-dichloropropane is two orders of magnitude lower than ATSDR's lowest comparison values. ATSDR has no cancer-based comparison value (CREG) for 1,2-dichloropropane because it currently considers the animal evidence to be "equivocal" or "limited", at best, as do both the International Agency for Research on Cancer (IARC) and NTP, the agency that produced the data in the first place (NTP, 1986). NTP and IARC currently classify 1,2-dichloropropane as "not classifiable" with regard to its potential carcinogenicity in humans. An MCL based on the "not classifiable" cancer classification would be higher by one or more orders of magnitude.
However, the current MCL is still 5 ppb, and EPA's MCLs are legally enforceable drinking water standards, whereas the comparison values and cancer classifications of ATSDR, NTP and IARC are not. A carbon filter was provided to the well owner known to have more than 5 ppb 1,2-dichloropropane in the well water. While ATSDR does not consider even the highest concentrations of 1,2-dichloropropane detected in drinking water to represent a potential public health hazard, this agency nevertheless recognizes that the action of providing a carbon filter to the residence was based on prudent public health policy.
Three additional contaminants (i.e., bromodichloromethane, chloroform, and dibromochloromethane) were detected in this same private well at levels that exceeded ATSDR's CREG comparison values (Table 4, Appendix C) in raw, unfiltered water; however, these same three contaminants were not detected after the water received treatment from the carbon filter. Because residents are drinking the filtered water rather than the raw, unfiltered water, they are not generally exposed to detectable levels of chloroform and the two by-products mentioned above. However, even the levels detected in raw, unfiltered water would pose no health hazard because, although these levels exceed ATSDR's CREGs by relatively slight margins, they are far below all other comparison values, including federal drinking water standards. (EPA's MCL for each of these three compounds is 100 ppb.) Recent drinking water studies in rodents have demonstrated that the actual carcinogenic potential of these compounds is much lower than the already low (i.e., < 0.0001) theoretical risk suggested by ATSDR's CREGs and the cancer risk assessments on which they are based. (The cancers on which these risk assessments and CREGs are based were produced in rodents force-fed high concentrations of the chemical in oil. However, these same cancers were not induced in animals treated ad libitum with the same chemicals in drinking water.)
No comparison values are available for calcium, magnesium, potassium and sodium (Table 4, Appendix C) because all of these elements are essential nutrients with low potential for toxicity (NRC, 1980). In fact, the estimated doses that would be associated with the highest detected concentrations of these elements in private well water surrounding the nursery site would be small relative to their respective recommended daily allowances (NRC, 1980; FNB, 1989). Hyperkalemia (potassium poisoning) is not even possible via dietary exposures alone, at least not in people with normal circulatory and renal function; it is usually a symptom of some pre-existing health problem such as Addison's disease or renal failure (NRC, 1980). In addition, high intake of potassium has a protective effect against the hypertensive effect of sodium. Sodium toxicity, on the other hand, is not generally associated with daily NaCl intakes less 30,000 milligrams/day (mg/day) (NRC, 1980).
Contaminants in On-Site Groundwater
Ingestion of on-site groundwater from monitoring wells has not occurred in the past and is not occurring currently. The maximum concentrations of benzene; beta BHC; chlordane; DDD; diazinon; and arsenic exceeded one or more of ATSDR's comparison values (Table 3, Appendix C). However, only chlordane was consistently detected in on-site temporary wells. The other compounds were each detected only once above ATSDR comparison values, and do not represent a potential public health concern.
The maximum detected concentration of chlordane of 200 ppb (Table 3, Appendix C) in a temporary well was an isolated value; all other detects were below all of ATSDR's noncancer comparison values, which incorporate a safety factor of 100 (ATSDR, 1994). In 1992, when the high of 200 ppb was detected in this on-site temporary well, no chlordane was detected in the other on-site temporary well. Chlordane was detected in two of three on-site wells tested in 1995, but at levels below 1 ppb. Chlordane has never been detected in private wells.
The contaminants listed in Table 9, Appendix C (Tank Pull Sampling Results-1992) were present at low concentrations, relative to most of ATSDR's noncancer comparison values. More importantly, these data only represent levels detected during a removal action. There was no direct exposure to the contaminants in water inside this underground storage tank before or after its removal in 1992.
Contaminants in On- and Off-Site Soils/Sediments
Few of the soil/sediment contaminants listed in Tables 5 through 8, Appendix C, exceed ATSDR's comparison values. Generally speaking, those that do (e.g., chlordane, benzo(a)pyrene, cadmium, and chromium in on-site soils; chromium in off-site soils; and chromium and vanadium in sediment) only exceed CREGs and EMEGs/reference dose evaluation guides (RMEGs) for pica children. (The only exceptions, arsenic and manganese, are discussed below.) However, neither the duration nor the magnitude of actual exposures to on-site soils will be comparable to the default exposure assumptions on which ATSDR's CREGs and EMEGs/RMEGs for pica children are based. ATSDR therefore concludes that, under site-specific conditions of exposure, none of the contaminants detected in soil or sediment are likely to pose a hazard to public health.
The maximum concentration of arsenic detected off site was an estimated 43 parts per million (ppm) in an isolated, surface soil sample, which is about twice ATSDR's chronic child EMEG of 20 ppm. Using default assumptions of exposure rate (i.e., daily ingestion of 200 milligrams [mg] soil), this maximum detected concentration would correspond to less than 9 micrograms arsenic/day (µg/day). This is at least an order of magnitude lower than typical dietary exposures and is comparable to average arsenic exposures from US drinking water, which usually contains less than 5 micrograms per liter (µg/L). Assuming a child body weight of 10 kilograms, this level of exposure would be comparable to the estimated human no observed adverse effect level (NOAEL) of 0.8 micrograms per kilograms per day (µg/kg/day) on which ATSDR's chronic minimal risk level (MRL) is based (ATSDR, 1993). (The chronic oral MRL of 0.3 µg/kg/day, which is based on exposure to arsenic in drinking water, rather than soil, contains a safety factor of 3.) More importantly, (1) historical evidence suggests that the carcinogenic, as well as the noncarcinogenic, effects of arsenic may exhibit a threshold at 200-400 µg/day, and (2) virtually all known cases of arsenical skin cancer have been associated with occupational exposure (Marcus and Rispin, 1988; Storher, 1991). Finally, because all 200 mg of the soil that a child might (hypothetically) ingest every day will not come exclusively from any single "hot spot," actual exposures to arsenic in soil are likely to be substantially less than the isolated, maximally-contaminated soil sample would imply. Therefore, ATSDR concludes that average, soil-related arsenic exposures surrounding the nursery site are unlikely to pose any hazard to public health.
Arsenic in on-site soils range from 0.7 to 2.3 ppm, and levels in sediment from off-site drainage ditches range from 0.7 to 1 ppm (Tables 6 and 8, Appendix C). None of the latter concentrations exceed ATSDR's child EMEG for chronic exposure. Therefore, ATSDR considers that, under site-specific conditions of exposure, the average doses of arsenic from the area surrounding the nursery site that might result from incidental or intentional soil ingestion are not likely to pose any hazard to public health.
The maximum detected concentration of manganese in on-site surface soil ranges from 2.1 to 650 ppm, which exceeds ATSDR's child RMEG (300 ppm) by a factor of 2.2 (Table 6, Appendix C). However, as mentioned previously, all of a child's soil-related exposure will not come from a single "hot spot". In particular, children's exposure to on-site soils and sediments are expected to be considerably less than to off-site soils. Manganese in off-site soils range from 15 to 68 ppm, and levels in sediment from off-site drainage ditches range from 2.4 to 110 ppm (Tables 7 and 8, Appendix C). None of the latter concentrations exceed ATSDR's child RMEG for chronic exposure. Therefore, ATSDR considers that, under site-specific conditions of exposure, the average doses of manganese from the area surrounding the nursery site that might result from incidental or intentional soil ingestion are not likely to pose any hazard to public health (ATSDR, 1997).
As stated above in the section on drinking water, ATSDR has no comparison values for many essential mineral nutrients because the potential for toxicity resulting from exposure to these substances in environmental media is usually quite low. For example, the estimated doses that would be associated with the highest detected concentrations of calcium, magnesium, potassium, and sodium in soils in Palm City would be less (usually much less) than 2 % of the respective recommended daily allowances.
ATSDR evaluates the health of a community living near a potentially contaminated site by considering the toxicity of the identified chemicals, defining a plausible completed pathway of exposure, and addressing the community's health concerns. The types of health data that are collected by state agencies and then reviewed may include disease incidence, cancer statistics, low birth weights, and developmental conditions. Individual state cancer registries collect data on reported cancers identified in populations and classify these reported cancer cases into different categories, such as skin, liver, breast, colon, etc. Depending on the type of data available, the rate of specific cancers can be determined for certain populations.
Citizens living near the Loxahatchee Nursery site were concerned with cancer resulting from possible exposures to contaminants identified on and off the site. Environmental sampling for on- and off-site groundwater, private well water, soil, and sediment have not identified any chemicals that would likely result in adverse health effects, including cancer. Water sampling analysis has been conducted at selected private wells since 1992. The chemical, 1,2-dichloropropane, was identified in one private well above EPA's MCL but not ATSDR's comparison values. This one residence is currently using filtered water to eliminate exposure. The chemical, 1,2-dichlorpropane, was also found in trace amounts in five other private wells, but not above health based comparison values. Therefore, no chemicals were identified at levels of health concern or increased risk for cancer.
Only health statistics data for Martin County for rates of "all-cancers" (not individual cancers) were available for review. Therefore, it was not possible to evaluate the incidence of cancers specific for the small community located around the site. While environmental contaminants may play a role in some types of cancers, other risk factors such as genetics, lifestyle, and socio-economic factors are known to have a profound influence on the development, diagnosis and treatment of disease. In the United States, the lifetime risk of developing cancer is approximately one in three, depending on the type of cancer (ACS, 1997). However, intervention activities including, improved diet, early detection, and better health care, have shown that individuals with certain types of cancers have remarkably improved survival rates today.
Community members expressed several concerns regarding the Loxahatchee Nursery site. ATSDR addressed each of the community concerns as follows:
Concern: contamination of private wells by pesticides leaching into the groundwater from the nursery site
Response: Since 1992, private wells in the Gull Harbor and Pelican Cove area have been sampled for hydrocarbons and pesticides. To date, no pesticides have been detected in any of the private wells sampled. The pesticide, chlordane, was detected once in 1992 in an on-site monitoring well at a level exceeding the ATSDR EMEG comparison value. Low levels of chlordane, slightly exceeding the most protective comparison values (CREG and pica child EMEG), were detected in on-site soils. ATSDR would not expect the low levels of chlordane detected in on-site soil to have a major impact on area groundwater in the future.
Five private wells indicated trace levels of the organic compound 1,2-dichloropropane and one private well exceeded the recommended MCL for this contaminant on several occasions. The source of the 1,2-dichloropropane is not known; however, samples from monitoring wells, soils, and sediments on site have not indicated this contaminant, which suggests the nursery is not the source. Regardless of the source of the 1,2-dichloropropane, the levels detected in private wells are not of health concern.
Overall, sampling of private well water indicates that the detected contaminants, including 1,2-dichloropropane, are currently not at levels of health concern. ATSDR recommends periodic sampling of private wells to ensure residents will not be exposed to constituents in the groundwater at levels of health concern in the future.
Concern: contamination of residential soil and contamination of surface water flowing from the site through the drainage ditches within the community
Response: In March 1998, EPA and FDEP performed limited sampling of residential soil and sediment from the drainage ditches. Low levels of VOCs were detected. The levels of these contaminants detected during this limited sampling event were all below ATSDR comparison values; therefore, ATSDR would not expect any adverse health effects from exposures to these contaminants in residential soil and the drainage ditches. Chlordane in sample SS03A and benzo(a)pyrene in sample SS09A were detected at a level that exceeded ATSDR comparison values; however, exposure to these contaminants is not expected to cause adverse health effects. Several metals (arsenic, cadmium, chromium, manganese, and vanadium) were also detected in soil and/or sediment samples on and off site; however, ATSDR would not expect any adverse health effects to occur from exposures to these metals in soil and/or sediment.
Concern: contamination of the site and surrounding area by the chemicals benlate and flusilazole
Response: On several occasions, the Martin County Health Department (MCHD) collected and analyzed private well water for the chemical, benlate (HRS, 1996c). On all occasions, benlate was not detected. During the March 1998 sampling event, both EPA and FDEP collected and analyzed groundwater, soil, and sediment samples for benlate. The EPA procedure tested for benlate as carbendazim. The benlate is converted to carbendazim in the EPA laboratory analysis procedure, so this procedure measures both benlate and carbendazim in the sample (ATSDR, 1998d). Because carbendazim was not detected in any of the samples, benlate is considered nondetect also.
FDEP sampled for additional contaminants during the March 1998 sampling event. One of the contaminants in the samples analyzed by FDEP, but not by EPA, is flusilazole. Flusilazole was not detected in any of the groundwater, soil, or sediment samples. However, the community voiced concerns during a public meeting in August 1998 over the analyses. The community was concerned that the arbitrary holding times for the samples had expired. While FDEP and ATSDR do not believe that holding the samples in the laboratory for an extra week compromised the data, ATSDR acknowledges the community's concern. The community also does not believe that the flusilazole analytical procedure was validated. ATSDR plans to request the flusilazole validated analytical procedure from FDEP. ATSDR is considering sampling at the site and testing for flusilazole once the Agency has reviewed the validated analytical procedure.
Concern: the incidence of cancer in the residential community surrounding the nursery
Response: The community living near the Loxahatchee Nursery is concerned with a perceived increase in the incidence of cancer. Environmental data were reviewed; however, no association between the detected chemicals and increased risk of developing cancer was identified. Cancer data specific for the small community around the Loxahatchee Nursery were not available for review. If future sampling demonstrates levels of contaminants that are of health concern, ATSDR will reevaluate this health concern. Of note, the MCHD plans to investigate cancer incidence.
Concern: the dangers to children playing on the site near the ponds and buildings
Response: In the Physical Hazards section of this public health assessment, ATSDR identified the physical dangers associated with the site. As mentioned previously, the Loxahatchee Nursery site is not currently fenced, thus making it easy for children to trespass on site. While the on-site pond is not viewable from the nursery's dirt road, children who realize it exists may gain access to this pond. The remaining structures on site are in a state of disrepair. ATSDR concludes that the on-site pond and dilapidated structures could pose a potential physical hazard to area residents, especially children, who trespass on site. Therefore, ATSDR recommends limiting site access to these hazards.
Concern: the future development of the site for residential housing
Response: The future use of the site has not been determined, although it is proposed to be
residential. In addition to determining if the site is free of contamination, other logistical issues
must be addressed before the area is developed. For instance, connections to the municipal water
and sewer system must be resolved (ATSDR, 1998a). While ATSDR is aware of these issues,
they are out of the purview of this public health assessment.
ATSDR recognizes that infants and children may be more vulnerable to exposures than adults in communities faced with contamination of their air, water, soil, or food. This vulnerability is a result of the following factors:
- Children are more likely to play outdoors and bring food into contaminated areas.
- Children are shorter, resulting in a greater likelihood to breathe dust, soil, and heavy vapors close to the ground.
- Children are smaller, resulting in higher doses of chemical exposure per body weight.
- The developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages.
Because children depend completely on adults for risk identification and management decisions, ATSDR is committed to evaluating their special interests at the Loxahatchee Nursery site, as part of the ATSDR Child Health Initiative.
Children who are the most likely to be exposed to environmental media at the Loxahatchee Nursery site include the children living in nearby homes. Exposures to media include:
- Groundwater: Children are exposed to area groundwater through the use of private well water.
- Sediment: Children could have been, and could continue to be, accessing the on-site pond and drainage ditches as well as the South Fork of the St. Lucie River.
- On-Site Soil: Children could have been, and could continue to be, exposed to nursery soil when trespassing on the site.
- Off-Site Soil: Children could have been, and could continue to be, exposed to nursery soil that was carried to off-site locations by the wind and during floods.
As indicated in the Toxicologic Evaluation section of this public health assessment, the concentrations of contaminants in private well water, sediment, and soil are not at levels of health concern for area residents, including children.