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Petitioned Public Health Assessment

Soil Pathway Evaluation

Isla de Vieques Bombing Range
Vieques, Puerto Rico


In 1999, a resident of Vieques asked (that is, petitioned) the Agency for Toxic Substances and Disease Registry (ATSDR) to determine whether the Navy's operations on Vieques expose residents to unhealthy levels of environmental contaminants. For the last 2 years, ATSDR has studied this issue extensively. The results of those studies appear in a series of reports known as public health assessments (PHAs). This PHA evaluates the soils of Vieques and addresses the public health implications of exposure to them. ATSDR's findings and the reasons supporting them are documented throughout this report, but the main conclusions are identified below.

Soil Characteristics

ATSDR evaluated the general soil characteristics of Vieques to identify:

  1. Whether the soils of Vieques have elevated levels of metals or other chemicals.
  2. Whether the soils of Vieques show evidence of contamination by Navy training activities.

To answer these questions, ATSDR evaluated the general soil characteristics of Vieques in several ways.

Public Health Evaluation

ATSDR identified two potential pathways of human exposure to chemicals in the soil of Vieques:

  1. Residents and visitors of Vieques can contact the soil in the residential portion of the island.
  2. Individuals can contact the soil when they enter the LIA.

ATSDR evaluated whether incidental ingestion or dermal contact with the soil would result in harmful health effects from either exposure pathway.

Overall Conclusions

Based upon a thorough evaluation of the soils of Vieques, including the soils of the residential area as well as the LIA, ATSDR concludes that Navy training activities have elevated the levels of some metals in soil at the LIA, however, residents and visitors of Vieques are not being exposed to harmful levels of contamination in those soils.


A request from a concerned individual to evaluate a site is received through a written document known as a petition.In May 1999, a resident of Isla de Vieques (Vieques), Puerto Rico, requested (petitioned, see text box for definition) the Agency for Toxic Substances and Disease Registry (ATSDR) to determine whether hazardous substances from the detonation of munitions at the United States Navy (Navy) bombing range on the island pose a public health threat. In August 1999, ATSDR conducted an initial site visit to Vieques to meet with the petitioner, tour the island and bombing range, and gather available environmental data. As a result of this site visit, ATSDR accepted the petition and since then has been investigating public health concerns related to the Navy's training activities on Vieques.

ATSDR is responding to this petition in a series of documents known as public health assessments (PHAs). PHAs examine chemicals that enter the environment, how they move through the environment, and the levels that residents might encounter. ATSDR then uses this information to determine whether residents or visitors are exposed to levels of contamination that might cause health problems.

This PHA addresses the public health implications of exposure to soil contaminants through incidental ingestion or dermal contact. More details about the soil pathway can be found in Section IV. Evaluation of the Soil Exposure Pathway. The issue of heavy metal uptake in plants and livestock from Vieques is addressed in Section V. Community Health Concerns.

Although this report focuses on soil quality issues, ATSDR has committed to evaluate other ways chemicals from the bombing range might affect public health. ATSDR has already addressed, or plans to address, the following public health issues:

An important aspect of the public health assessment process is defining and addressing health concerns of community members. Throughout the process ATSDR has been, and will continue to work with the community to define specific health issues of concern (see Section II.G). Discussion with community members has also helped define ways in which ATSDR can provide educational materials and information to protect the public health of Vieques residents.


Vieques is the largest offshore island in the Commonwealth of Puerto Rico. Vieques is 20 miles long, 4.5 miles at its widest point, and about 33,000 acres (or 51 square miles) in area. Figure 1 shows the location of Vieques and surrounding islands. As the figure illustrates, the nearest island to Vieques is the main island of Puerto Rico, approximately 7 miles to the west. The island of Culebra is roughly 9 miles north. St. Thomas, St. John, St. Croix, and other U.S. Virgin Islands are all at least 20 miles northeast and southeast from Vieques.

The highest point on the western half of Vieques is Monte Pirata (987 feet above sea level) and the highest point on the eastern half is Cerro Matias (450 feet above sea level). Other than these peaks, the Vieques terrain includes low rounded hills and an east-west ridge running through the center of the island. The average elevation of Vieques is approximately 246 feet above sea level (Cherry and Ramos 1995; Torres-Gonzalez 1989).

A. Land Use

The detailed map in Figure 2 illustrates land use in Vieques. The figure depicts the island in three separate sections, each of which is described in greater detail below:

East of the EMA is the AFWTF (3,600 acres), which as Figure 2 shows, is further divided into three smaller sections of land:

B. Demographics

ATSDR examines demographic data (i.e., population information) to determine the number of people potentially exposed to environmental chemicals, and to determine the presence of any sensitive populations, such as women of childbearing age, children, and the elderly. Demographic data also provide details on population mobility which, in turn, helps ATSDR evaluate how long residents might have been exposed to environmental chemicals.

Table 1 summarizes the 2000 US Census Bureau demographic data for Vieques. As the table shows, the 2000 Census reported that 9,106 people live on Vieques. This figure includes residents on both the residential area and Navy property. Table 1 also specifies the number of residents in three potentially sensitive populations: women of childbearing age, children, and the elderly. According to several anecdotal accounts, the population of Vieques is not highly mobile; many are lifelong residents of the island.

As noted previously, most of the residents of Vieques live in the two largest towns on the island, Isabel Segunda and Esperanza. Although these towns are located relatively close to the Navy property, they are several miles removed from the LIA. Approximately 7.9 miles (12.7 kilometers) of Navy owned land provides a buffer zone between the LIA and populated areas of Vieques.

C. Climate

Vieques lies in the path of the easterly trade winds (i.e., winds blowing from east to west). The climate is tropical-marine, with temperatures averaging about 79 Fahrenheit (26.3 Celsius). Annually, the temperature ranges from an average of 76 Fahrenheit (24.6 Celsius) in February to 82 Fahrenheit (28 Celsius) in August. The average amount of precipitation is about 45 inches a year. The western part of the island receives a higher amount of rainfall (about 50 inches a year) than the eastern section (about 25 inches a year). The rainy season is from August through November while the remainder of the year is drier. Tropical storms are common from June to November (NCDC 1985-1994; Torres-Gonzalez 1989).

African Dust Storms

Through the natural occurrence of African dust storms, Vieques, together with the mainland of Puerto Rico and the southeastern United States, receive in the summer an increase of airborne dust particles. Each year, large quantities of dust from the Sahara Desert and Sahel region in Africa are transported at high altitudes to the Caribbean Sea (USGS 2000). These dust storms can transport minerals, chemicals, bacteria, fungus spores--and possibly viruses and insects. African dust is comprised mainly of quartz, but also of other minerals, that are common in soil (Prospero 1999). Lead, iron, mercury, and beryllium have been detected in samples of African dust taken from the Virgin Islands, Barbados, Miami (Florida), and the Azores. Pesticides associated with pesticide spraying in the Sahel region have also been detected in the dust (Ballingrud 2000).

D. Geology

Alluvial deposits are sediment deposited by flowing water.Vieques was formed from volcanic and other igneous rock. The island bedrock is mostly granodiorite, quartz diorite, and some lavas. Figure 3 is a generalized geologic map of Vieques identifying the island's geologic units (rock formations). On most of the western half as well as the central portion of the eastern half of the island, the bedrock is exposed and weathered. Because of the weathering of the bedrock, gravel, sands, and finer particles wash downhill during storms. Over the years this material has gathered in valleys near the ocean, forming alluvial deposits (see text box for definition). The alluvial sedimentary deposits generally consist of a mixture of gravel, sand, silt, and clay. Other portions of Vieques have ancient marine deposits from a time when the island was submerged. Today these deposits reveal areas with some limestone, sandstone, siltstone, and other sedimentary rocks at the surface.


Soils often form from the weathering and breakdown of the underlying rock or "parent material." Soils may be formed by the buildup of wind- or water-borne particles or by the addition of new minerals by naturally occurring chemical processes within the soil. There are many differing types of soil that form in different climates and on differing underlying parent materials. Five parameters, known as soil forming factors, contribute to the type of soil that can be found in an area: parent material (i.e., the geology that is present), relief (i.e., topography), organisms/microorganisms, climate, and time (Jenny and Hans 1941).

Analyzed as oxides, granodiorite and quartz diorite typically range from about: 61-66% silicon dioxide, 16-17% aluminum oxide, 2-3% ferric oxide, 2-4% ferrous oxide, 1-3% magnesium oxide, 3-6% calcium oxide, 3-4% sodium oxide, and 2-3% potassium oxide (after Travis 1955).The natural soil on Vieques is a direct product of the island's bedrock, which as indicated above, is mostly granodiorite, quartz diorite, some volcanic lavas, and marine sedimentary deposits such as limestone. Soil type can vary according to topography or location. For example, because of differing soil-moisture conditions--which lead to differing rates and kinds of chemical and physical weathering and soil forming reactions--soil found on the top of a hill would be slightly different from that found in a valley. Organisms and microorganisms living in the soil participate in the soil formation process by extracting some chemicals, which they use as nutrients, and depositing others. Climate also affects the type of soil present. Soil found in a tropical-marine climate, such as Vieques, is different from soil in an arid climate. Soil is also a function of time, or how long the processes (e.g., erosion, deposition, weathering, and clay formation) have been at work.

Rocks are a natural source of the chemicals that are found in soil. Most rocks are formed from elements such as oxygen, silicon, aluminum, iron, magnesium, calcium, potassium, and sodium (USGS 1997). Chemical and physical processes break down the rocks and form minerals that are characteristic of the parent material. But human influences, such as agricultural processes and Navy training exercises at the LIA can also contribute to the chemicals found in the soil. Determining whether a chemical is present as a result of natural or human sources is sometimes difficult because frequently, it can be a combination of both.

Ninety-two elements occur naturally in our environment (USGS 2001a). Some of these elements are essential for life, such as iron and magnesium. Others are nonessential and can even be harmful if present in high enough concentrations (e.g., arsenic, cadmium, lead, and mercury). Some elements are required for life at certain levels, but can be harmful in concentrations that are too high (e.g., fluorine, copper, selenium, and molybdenum) (USGS 2001b).

E. Hydrogeology

All the groundwater on Vieques comes from rain that falls on the island. The rain runs downhill as intermittent stream runoff or it seeps into the soil and underlying deposits. Water is found in two main areas: (1) the upper portion of the bedrock and sedimentary rocks, and (2) the alluvial deposits. Water in pore space, cracks, and fractures in the bedrock eventually flows to the ocean or into alluvial deposits. Esperanza valley is the largest alluvial valley in Vieques and holds the most water.

Water Use

Most of the residents of Vieques currently receive their drinking water supply from the mainland of Puerto Rico through an underwater pipeline. The water is collected and treated on the main island of Puerto Rico, then piped into the distribution system through an underwater pipeline. This water originates in the mountains of the main island of Puerto Rico and is not affected by activities at the bombing range on Vieques. In addition, private groundwater wells and rainfall collection systems may still be used today to augment water supplies in some households and businesses.

F. Navy Operational History

The Navy has occupied portions of Vieques since 1941. In 1960, the Navy established targets on Vieques and began bombing practice (Navy 1990). The use of the LIA for air to ground and ship to shore training increased after the closing of the Culebra Island range in the mid-1970s. Currently, the Navy owns roughly the eastern half of the island--the EMA and AFWTF (see Figure 2). The Navy facilities are under the command of the Roosevelt Roads Naval Station on the mainland of Puerto Rico.

Ordnance Type and Use

Range utilization statistics data from 1983 to 1999 indicate that the Navy and other parties conducted exercises on Vieques between 159 and 228 days per year, with the total number of days not varying considerably from one year to the next. Generally, Navy training exercises were most frequent in February and August with fewer exercises in April, May, November, and December. The range utilization statistics suggest that, on average, 1,862 tons of ordnance were used at Vieques annually between 1983 and 1998. This ordnance, on average, contained 353 tons of high explosives (Navy 1999).

Live ordnance have not been used on Vieques since April 19, 1999, when two 500-pound bombs were accidentally dropped near OP-1, killing a civilian guard. In January 2000, the decision was made that the Navy could resume training on Vieques. The training is limited to 90 training days per year and the use of nonexplosive ordnance only. In May 2000, the Navy resumed training.

To varying degrees metals and metallic compounds are present in the munitions used on Vieques (see text box on the following page for descriptions of ordnance types). Rockets contain metals and metallic compounds in the initiator, igniter, propellant, and motor. A projectiles' body assembly and nose fuze are made of metals and metallic compounds. Both live and practice bombs contain metals and metallic compounds in the bomb body, base plug, suspension lug, fins, tail, fuze, and signal cartridge. The decoy, parachute, and simulator flares used on Vieques contain metals and metallic compounds in the ignition, first fire, flare slurry, friction material, and flare.

Certain pyrotechnic devices, such as illuminating flares and white phosphorous mortar rounds, are also used on Vieques for smoke generation. The flares contain sodium nitrate and magnesium, which when ignited produce magnesium oxide (magnesium hydroxide when wet), sodium oxide, nitrogen, carbon dioxide, carbon monoxide, and water. Upon contacting air, white phosphorous burns immediately, producing phosphorus pentoxide, which becomes phosphoric acid when wet (Young 1978).

Ordnance Types: The three types of flares used on Vieques are decoy, parachute, and simulator. All three are launched from aircraft. Decoy flares are fired during evasion tactics when the aircraft is threatened by enemy heat-seeking missiles. Parachute flares are launched to provide nighttime illumination of surface areas, often during search and attack operations. Simulator flares are designed to produce effects that imitate the appearance of combat weaponry. -- Illuminating projectiles are designed to eject a pyrotechnic candle to a certain point to allow visual observation. The projectiles that are now used on Vieques are inert target practice projectiles filled with an inert material without a signal (i.e., spotting) charge or a fuze. -- General purpose bombs are dropped from aircraft. They consist of a bomb body, nose and/or tail fuzing, and either a conical fin assembly or a retarded fin assembly. The explosive components of the bombs include 2,4,6-trinitrotoluene (TNT), cyclotrimethylene trinitramine (RDX), methyl-2,4,6-trinitrophenylnitramine (tetryl), cyclotetramethylene tetranitramine (HMX), ammonium picrate (Explosive D), and various combinations of these chemicals. -- Practice bombs are dropped from aircraft for target practice and are designed to simulate the ballistic properties of service bombs. They are manufactured with either solid cast-metal bodies or thin sheet metal containers that can be filled with sand or concrete. Practice bombs do not contain a main explosive load. They can, however, contain a small amount of explosive and reactive material in a signal cartridge (i.e., spotting charge) thus providing a visual indication of the impact. -- The Navy uses two rockets on Vieques. Both are aimed at the target and fired; once the rocket has been fired, the trajectory cannot be changed. A variety of warheads and fuzes were used on these rockets, depending on the tactical situation. Today, inert practice warheads are used for training and several smoke-producing warheads are used to mark the targets. -- Source: Navy 2001b

An explosive is any substance that can be made to produce a volume of rapidly expanding gas during a brief period.Two types of explosives (see text box for definition), described below, were commonly used at Vieques, each with a different set of byproducts from the explosion reaction (Young 1978):

During a February 19, 1999 training exercise, depleted uranium ammunition was inadvertently loaded aboard two U.S. Marine Corps aircraft (NRC 2000). The pilots fired 263 rounds of ammunition armed with depleted uranium penetrator projectiles on the LIA. The Navy has committed to recover all detectable depleted uranium penetrators, and as of August 2002 reported to have recovered 116 equivalent units. During June 6-15, 2000, the Nuclear Regulatory Commission (NRC) conducted an inspection of Vieques to determine whether the depleted uranium rounds contaminated the environment, thus creating a potential source of radiation exposure for Vieques residents. The NRC concluded that depleted uranium had not spread to areas outside the LIA. Thus the public had not been exposed to depleted uranium contamination or other radiation above normal background (naturally occurring) levels (NRC 2000). ATSDR has reviewed the NRC report and concludes that the background levels of radiation detected on Vieques do not present a public health hazard.

G. ATSDR Involvement at Vieques

Since its 1999 receipt of the petition requesting an evaluation of public health issues on Vieques, ATSDR has worked extensively to characterize and to respond to community needs. The following is a summary of ATSDR's past Vieques involvement:

H. Summary of the Available Soil Sampling on Vieques

In 1972, personnel from US Geological Survey (USGS) and the Puerto Rico Department of Natural Resources (PRDNR) jointly surveyed surface soil across Vieques to evaluate the metallic resource potential of the island (see Figure 4 for soil sample locations) (Learned et al. 1973). A total of 420 soil samples were taken and analyzed semi-quantitatively for metals (1). In 1992, USGS released a reconnaissance geochemical survey with analytical results for stream sediment and soil samples from the Puerto Rican mainland, Culebra, and Vieques (Marsh 1992). The source for the Vieques soil data was the 1972 USGS and PRDNR survey. The sediment data for the mainland of Puerto Rico was generated through a cooperative sampling effort between USGS and PRDNR that began in the 1970s. A total of 2,852 stream sediment samples were analyzed for metals (2).

In May 1978, the Naval Surface Weapons Center obtained and analyzed soil samples for explosive compounds from two areas within the EMA and four areas within the LIA (Hoffsommer and Glover 1978). At the same time, soil collected from one area within the EMA and five areas within the LIA was analyzed for explosion combustion products (Lai 1978) (3).

In October 1998, to document existing environmental conditions at a section of the former NASD's buffer zone proposed for expansion of the Vieques Municipal Airport, a contractor for the Navy collected five soil samples (see Figure 4 for locations) (PMC 1998). These samples were analyzed for volatile organic compounds, semivolatile organic compounds, pesticides, polychlorinated biphenyls, and metals.

In August 1999, a contractor for the Navy collected and analyzed for explosive compounds 32 surface soil samples along EMA's western border (see Figure 4 for soil sample locations) (CH2MHILL and Baker 1999). Twenty-one of the samples were collected from storm drains (i.e., culverts that are normally dry and only contain water during rain events); the remaining 11 were from areas adjacent to the monitoring wells.

From May 1999 to April 2000, personnel from Servicios Científicos y Téchnicos, Inc. (Garcia et al. 2000) collected and analyzed soil and sediment samples from 55 Vieques locations for metals and other inorganic compounds (Garcia et al. 2000). Of these, 44 samples were collected from the LIA; specifically, areas of direct impact, targets areas, and nearby areas. Five were collected from the Punta Este Conservation Zone and six were taken from the residential area. But ATSDR does not have access to the entire sampling data set. Only the highest and second-highest concentrations were reported for a total of 25 sample locations within the LIA (4) (see Figures 4 and 5 for soil sample locations).

In June 2000, at ATSDR's request, a Navy contractor collected and analyzed 37 surface soil samples within the LIA (specifically, from targets and drainage features and low lying areas which would collect stormwater runoff) and within conservation zones immediately adjacent to the LIA (see Figures 4 and 5 for locations) (CH2MHILL 2000a). Five of the sites specifically represented areas where the protestors lived from April 1999 to May 2000. The samples were analyzed for metals and explosive compounds.

In December 2000, a Navy contractor conducted a background (naturally occurring) sampling program in support of the Navy's Installation Restoration Program at the former NASD (CH2MHILL 2001). Samples of surface and subsurface soils, groundwater, surface water, and sediment were collected at various locations in the former NASD thought to be unaffected by man's activities. A total of 26 surface soil samples were collected and analyzed for metals (see Figure 4). A draft report summarizing the results of that investigation was released June 15, 2001.

I. Quality Assurance and Quality Control

To prepare this PHA, ATSDR reviewed and evaluated information provided in the referenced documents. The environmental data are from reports produced by many parties, including USGS in cooperation with PRDNR, the Navy, and Servicios Científicos y Téchnicos, Inc. The limitations of these data have been identified in the associated reports, and are restated in this document, as appropriate. The sampling procedures, analytical methods, and detection limits established for those investigations were consistent with the studies' objectives. Quality assurance and quality control measures were not available for the older data (i.e., Learned et al. 1973; Hoffsommer and Glover 1978; and Lai 1978) and data collected by Servicios Científicos y Téchnicos, Inc. (Garcia et al. 2000). ATSDR determined that the quality of environmental data available in the Vieques site-related documents constitutes an adequate basis for public health decisions. All available soil sampling data was considered during the public health assessment process.


A. Background

As noted in Section II.D Geology, soils often form from the weathering and breakdown of the underlying rock or "parent material." Chemical and physical processes break down the rocks and form minerals that are characteristic of the parent material. Therefore, the natural soil on Vieques is a direct product of the island's bedrock, which is mostly granodiorite, quartz diorite, some volcanic lavas, and marine sedimentary deposits such as limestone.

What are the chemical characteristics of soils of the different geologic units on Vieques?

Chemicals are often measured in parts per million (ppm). To help visualize the amount of chemical this represents, imagine an average 3-bedroom house, it would take about 1 million marbles to cover the floors of the house. One part per million would be one of the marbles on one of the floors (USGS 2001a).To compare and contrast the soils of Vieques, the soil samples were differentiated based on the underlying parent material (i.e., the rock formations or geologic units) on which they developed. ATSDR compared the constituent metals detected in the soil that developed on one geologic unit to the metals in the soil in the other geologic units. Comparisons were considered statistically significant (i.e., different) if there was less than 5% probability that the difference occurred by chance (i.e., p <0.05). Figure 3 illustrates the location of the generalized geologic units on Vieques used for this phase of the analysis (modified from Torres-Gonzalez 1989).

Exhibit 1. Comparison of Significantly Different Metals in Kv and non-Kv Geologic Units

Metal Kv Geologic Unit non-Kv Geologic Unit Metal Kv Geologic Unit non-Kv Geologic Unit






Boron 12.5 158 10.8 258 Nickel 23.8 174 14.3 279
Chromium 70.9 173 49.2 280 Scandium 19.2 159 14.4 257
Cobalt 15.6 174 11 279 Titanium 4,580 159 3,230 257
Iron 54,200 174 40,300 279 Vanadium 194 174 143 279
Lead 25.7 173 12 280 Yttrium 26.1 159 20.9 257
Magnesium 14,700 159 9,950 261 Zinc 136 171 42.1 269
Manganese 1,360 173 1,150 280 Zirconium 95.8 159 78.8 257

Using the data collected by USGS and PRDNR in 1972 (Learned et al. 1973), ATSDR compared the chemical characteristics of the KTd geologic unit to the Tl geologic unit. This comparison is necessary for establishing the inherent chemical differences between these two units and will be useful in the discussion of the second approach ATSDR used to determine whether the soils of the LIA contain elevated levels of heavy metals (Section III.C). As shown in Exhibit 2, several metals were statistically significantly different.

Exhibit 2. Comparison of Significantly Different Metals in Kv and Tl Geologic Units

Metal KTd Geologic Unit Tl Geologic Unit Metal KTd Geologic Unit Tl Geologic Unit






Barium 917 212 155 8 Strontium 295 205 200 6
Cobalt 10.5 209 6.8 6 Titanium 3,290 212 2,200 8
Iron 41,900 212 27,100 8 Vanadium 149 212 84.4 8
Manganese 1,250 212 639 9  

B. Comparison of Vieques to the Mainland of Puerto Rico and the United States

Can the soil of Vieques be compared to the mainland of Puerto Rico?

Based on available information, only a generalized comparison can be made. While soil data are available for Vieques, the only area-wide, chemical characterization data available for the mainland of Puerto Rico are stream sediment sampling collected by USGS and PRDNR (Marsh 1992). The stream sediment samples were collected from active stream channels in drainage basins ranging in size from less than 1 square kilometer to less than 10 square kilometers. The objective of this geochemical sampling program was to characterize the distribution of commonly occurring elements and metals throughout the mainland of Puerto Rico.

Sampled stream sediments are representative of the soil and their parent material (e.g., the geologic substrates of that drainage basin) as well as other factors (e.g., human activity, etc.) that could have affected that drainage basin. The stream sediments are comprised of granular material derived from erosion, stream transportation, and deposition of the soil and drainage-related geologic deposits. The physical and chemical process responsible for the erosion, transportation, and deposition of those sediments could introduce several changes to the overall composition of the sediments as compared to the soil from which they were derived.

Ideally, ATSDR would compare the soil on Vieques to soil on the Puerto Rico mainland. But because comparable area-wide data for the mainland are not available, ATSDR determined that comparing the soil on Vieques to the sediment on the mainland of Puerto Rico would still serve to point out generalized similarities or differences between the two areas. Given the inherent differences between the two media, the following can be noted: the soil of Vieques has higher concentrations of antimony, arsenic, cadmium, calcium, manganese, molybdenum, silver, strontium, and yttrium than the stream sediment samples collected throughout the mainland (see Table 2).

However, when ATSDR compared the background sediment samples collected in the former NASD (CH2MHILL 2001) to the sediment data collected on the mainland of Puerto Rico (Marsh 1992), the levels of metals from the former NASD are lower or at the lower end of the range than those detected on the mainland, with the exception of calcium and sodium (see Table 3). Note that a small number of background sediment samples at the former NASD (n = 6) are being compared to a much larger sample set from the mainland of Puerto Rico (n = 2,852). In addition, the samples were collected and analyzed using differing procedures and methods.

How does the soil on Vieques compare to the average soil concentrations in the United States?

Vieques soil is generally comparable to the soil across the United States, especially areas underlain by igneous or volcanic rocks. A statistical comparison between Vieques and the United States was not conducted. Instead, this information is referenced to provide additional insight into the metals and other chemical concentrations detected on Vieques. The United States data represent background soil concentrations taken from uncontaminated areas across the conterminous (i.e., contiguous) United States (Shacklette and Boerngen 1984). The average concentrations for several of the metals were higher on Vieques than the average on the United States. Nevertheless, only the maximum concentrations of copper, iron, lead, tin, and zinc detected on Vieques were outside the ranges found throughout the United States (see Table 2).

As noted in Section II.H Summary of the Available Soil Sampling on Vieques, the soil samples collected by USGS and PRDNR in 1972 (Learned et al. 1973) may be as much as 4-fold higher than the true values. Therefore, any apparently "elevated" levels in comparison to background levels in the United States may be a result of this high-bias in the USGS/PRDNR data (the only island-wide soil sampling available for Vieques), rather than being truly elevated.

Regardless, as noted in Section II.D Geology, soils contain chemicals that are characteristic of the underlying rock, and the metal concentrations observed in the soil of Vieques are consistent with those observed in areas of relatively low-level mineralization (natural mineral enrichment through a variety of geologic processes) in igneous or volcanic rock.

C. Comparison of the LIA to the Remainder of Vieques

Do the soils of the LIA contain elevated levels of heavy metals?

ATSDR attempted to answer this question using two different approaches: (1) by comparing concentrations of chemicals detected at the LIA to the remainder of Vieques and (2) by comparing concentrations of chemicals detected at the LIA to background soil samples in the NASD. Both approaches yielded useful but slightly differing conclusions and each may be based upon data (high-biased) or assumptions (correlations of geologic/soil types) that may result in conclusions that are not entirely accurate.

Overall, it appears that the soils of the LIA have been influenced by Navy training activities and contain elevated levels of heavy metals. Given the potential problems associated with the data and assumptions used, additional background soil sampling in the LIA would be necessary to confirm the validity of this conclusion. Although, ATSDR realizes collecting background samples from the LIA may no longer be possible. The next section, Section IV. Evaluation of The Soil Exposure Pathway, describes the methods ATSDR used to determine that despite the apparent elevation in chemical concentrations at the LIA, residents and visitors of Vieques are not being exposed to harmful levels of chemicals in the soil.

Has the LIA become more contaminated with time?

ATSDR attempted to compare soil samples collected from the LIA in 1972 (Learned et al. 1973) to soil samples collected from the LIA in 2000 (CH2MHILL 2000a), to determine if this 28-year interval of Navy training had significantly increased the level of contamination at the LIA. However, given that the data collected by USGS and PRDNR in 1972 appears to be elevated by as much as 4-fold higher than the true values (as described in Section II.H), this comparison became invalid.

D. Movement of Contamination from the LIA to the Residential Area

Is there a spatial pattern that indicates that metals are moving from the LIA to the residential area?

No. The available data do not indicate a pattern of high to low concentrations from east to west. Thus, this data set does not provide evidence indicating airborne transport of metals from the LIA to the residential area. Further analysis of this issue is being conducted by ATSDR using computer air transport models and will be presented in a separate air pathway evaluation (see Sections I and VIII).

To answer this question, ATSDR plotted on a map the locations of metal concentrations detected on Vieques. All of the studies, except the 1978 investigations (Hoffsommer and Glover 1978 and Lai 1978), identified their sampling locations either by latitude and longitude or on a figure. But only the reconnaissance geochemical survey conducted by USGS and PRDNR (Learned et al. 1973) collected samples from across the entire island. Therefore, most of the interpretations from this analysis are based on these data. As noted previously, it is reasonable to assume that there is internal consistency within the 1973 data and thus, those data are suitable for use in an evaluation of the relative spatial distribution of detected levels.

ATSDR generated chemical-specific maps for the metals that are found in munitions. None of the spatial maps showed a pattern beginning with high concentrations in the LIA and decreasing concentrations tapering off to the west of the island. Spatial maps were not generated for explosive compounds because the only detections were located at the LIA. Sampling for explosives was, however, conducted along the western border of the EMA in 1999, and none were detected (CH2MHILL and Baker 1999).

Although a spatial pattern describing a progressive east to west trend is not shown in the chemical-specific maps, other patterns are shown. For example, a western concentration of the highest levels of strontium detected is shown in Figure 6. Barium shows a similar western concentration and both chemicals seem to show an association with the areas underlain by granodiorite and quartz diorite (the KTd geologic unit).

A geologic association between the areas underlain by the undivided sedimentary rocks (the Tl geologic unit) and the occurrence of the highest detections of calcium is illustrated in Figure 7. Both vanadium and zinc show a geologic association with areas underlain by the marine sandstones and lavas (the Kv geologic unit), although the association is not a clearly developed as the calcium-Tl association.

Examination of the distribution of detected levels of the other metals does not show any clear pattern, trend, or association. This random distribution of detected levels is illustrated in Figure 8 for chromium. A similar random distribution is also exhibited by the spatial distribution of the detected levels of cobalt, copper, iron, magnesium, manganese, nickel, lead, titanium, yttrium, and zirconium.

1. When ATSDR compared the metal concentrations in soil samples collected from the former NASD during this effort to background (naturally occurring) soil samples recently collected from the former NASD (CH2MHILL 2001), the data collected by USGS and PRDNR was found to be higher, sometimes by 4-fold. Barium and calcium differ from this pattern for unknown reasons. Since sampling locations from both events were from areas unaffected by the Navy training activities, it would appear that the older data is artificially elevated (i.e., higher than the true values). Another indication is that for those metals analyzed and detected in all samples, the minimum values obtained during the USGS/PRDNR study are higher that the minimum values obtained during the recent background study, even though the minimum detection levels were higher than those used when the background analyses were performed. If there were no high-bias in the data reported in 1973 then several of the samples collected should have been reported as not detected. These differences are probably due, in part, to differing analytic or sampling methods. However, regardless of the reason(s) for the apparent differences, the higher values were used by ATSDR to evaluate potential health effects.
2. Please see the discussion "Can the soil of Vieques be compared to the mainland of Puerto Rico?" in Section III.B for an explanation of ATSDR's use of sediment data.
3. The laboratory that analyzed the samples noted that "a completely positive identification was not possible due to the extremely low concentrations found" (Hoffsommer and Glover 1978). They further note "if these explosives are present, the concentrations do not exceed the values reported here." ATSDR evaluated the chemical concentrations as reported to be most protective of human health; however, this should not be interpreted as validation of the laboratory study's results.
4. ATSDR utilized the available data with certain limitations. In a statistical comparison of this data to the other data collected on the LIA (Learned et al. 1973; CH2MHILL 2000a), nine of the 20 chemicals were significantly different (higher, p <0.05): ammonia, barium, cadmium, copper, lead, mercury, nickel, nitrate/nitrite, and zinc. This does not imply anything is amiss with the data; it simply means that using only the highest and second highest detections rather than the complete data set would skew any results. Therefore, these data could not be used in the statistical analyses. They were, however, used to form conclusions during the public health evaluations.

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