VII. Conclusions

Soil Characteristics

• After evaluating the soil geologically to identify any chemical trends between geologic units (e.g., rock formations) on Vieques, ATSDR concluded that significant differences existed in the metal composition of soils developed on the different geologic units. The soil developed on a complex assemblage of marine sandstones, siltstones, conglomenates, lava, and tuff. The tuff (the Kv formation) is the most dissimilar geologic unit, with significantly different concentrations of 14 metals. The soil developed on the alluvial sands, silts, and gravels (the Qa formation) is similar to the soil developed on other geologic units, with no significantly different metals. This indicates that the soils of Vieques are strongly influenced by the constituent chemicals of their parent materials.
• ATSDR compared the quality of the soil on Vieques with the sediment of the Puerto Rican mainland. After acknowledging the inherit differences between the two media, ATSDR noted that 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 of Puerto Rico. However, when ATSDR compared the background sediment samples collected in the former NASD to the sediment data collected on the mainland of Puerto Rico, the levels of metals from the former NASD are lower or in the low end of the range.
• ATSDR also compared the quality of the soil on Vieques with background soil concentrations within the United States. A statistical comparison was not conducted, but the average concentrations for several of the metals were noted to be higher on Vieques than the averages on the United States. The maximum concentrations of copper, iron, lead, tin, and zinc detected on Vieques were outside the ranges found throughout the United States. However, the levels detected on Vieques are not inconsistent with what one would expect from soils also underlain by igneous or volcanic rocks.
• ATSDR evaluated whether Navy training activities have elevated the levels of metals in the soils of the LIA. To do this, ATSDR (1) compared concentrations of chemicals detected at the LIA to the remainder of Vieques and (2) compared concentrations of chemicals detected at the LIA to background soil samples in the former NASD. The results of the evaluations indicate that the soils of the LIA have been influenced by Navy training activities and contain elevated levels of heavy metals. However, the concentrations of the chemicals in the soil are not at levels that pose an adverse health threat (see the Public Health Evaluation section).
• ATSDR evaluated general spatial trends for specific metals to identify whether a spatial pattern indicated chemicals are moving from the LIA to the residential area. 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 for airborne transport of metals from the LIA to the residential area.

Public Health Evaluation

ATSDR concludes that the levels of the metals found in the soil on Vieques would not result in harmful health effects for either adults or children who might incidentally ingest or come in contact with the soil while living on Vieques or while living on the LIA for a year. ATSDR has categorized this site as having no apparent public health hazard from exposure to soil on Vieques (definitions of public health categories are included in the glossary in Appendix B).

• ATSDR compared the chemicals detected in the soil on Vieques to conservative comparison values. Only seven metals (arsenic, cadmium, chromium, iron, manganese, lead, and vanadium) were detected above comparison values. All other chemicals were detected at concentrations too low to be of health concern for anyone (adults and children) incidentally ingesting or contacting the soil. After evaluating in greater detail the seven metals detected above comparison values, as well as mercury, ATSDR reached the following conclusions:
• Exposure to arsenic in soil on Vieques is not expected to result in harmful health effects because (1) the estimated exposure doses from incidental ingestion for adults and children are below the conservative health guideline for adults and below levels of health effects documented in the toxicological literature for children and (2) the small amount of arsenic that can be absorbed through the skin is not likely to result in any serious internal effects.
• Exposure to cadmium in soil on Vieques is not expected to result in harmful health effects because (1) the estimated exposure doses from incidental ingestion for adults and children are below the conservative health guideline for adults and below levels of health effects documented in the toxicological literature for children and (2) virtually no cadmium can enter the body through the skin.
• Exposure to chromium in soil on Vieques is not expected to result in harmful health effects because (1) the estimated exposure doses from incidental ingestion for adults and children are below the conservative health guideline for adults and below levels of health effects documented in the toxicological literature for children and (2) very little chromium will enter the body through contact with the skin.
• Exposure to iron in soil on Vieques is not expected to result in harmful health effects because (1) the estimated exposure dose from incidental ingestion for adults is below the conservative health guideline, (2) a child's estimated daily consumption is below levels known to result in childhood poisoning, and (3) only a minimal amount of iron is assumed to enter the body through the skin.
• Exposure to lead in the soil on Vieques is not expected to result in harmful health effects because (1) the estimated exposure doses from incidental ingestion for both adults and children are below levels of health effects documented in the toxicological literature, (2) the resulting child blood lead level is below CDC's health guideline, and (3) only small quantities of lead can be absorbed by the body through the skin, and what is absorbed represents a much smaller amount than that absorbed via ingestion.
• Exposure to manganese in soil on Vieques is not expected to result in harmful health effects because (1) the estimated exposure doses from incidental ingestion for adults and children are below the conservative health guideline for adults and below levels of health effects documented in the toxicological literature for children and (2) the increased exposure expected to result from dermal contact is below the NOAELs documented in the literature.
• Exposure to mercury in soil on Vieques is not expected to result in harmful health effects because (1) the estimated exposure doses from incidental ingestion for both adults and children are below levels of health concern documented in the toxicological literature and (2) the increased exposure expected to result from dermal contact is at least an order of magnitude lower than the reported NOAELs documented in the literature.
• Exposure to vanadium in soil on Vieques is not expected to result in harmful health effects because (1) the estimated exposure doses from incidental ingestion for adults and children are below the conservative health guideline for adults and below levels of health effects documented in the toxicological literature for children and (2) due to its low solubility, vanadium is not considered to be readily absorbable through the skin.
• ATSDR also conducted a public health evaluation specific to the protestors, who from April 1999 to May 2000 lived on the LIA. ATSDR compared the chemicals detected in the soil on Vieques to conservative comparison values. Only two metals (arsenic and iron) were detected above comparison values. All other chemicals were detected at concentrations too low to be of health concern for anyone (adults and children) incidentally ingesting or contacting the soil. After evaluating in greater detail the two metals detected above comparison values, as well as mercury, ATSDR reached the following conclusions:
• Exposure to arsenic in soil on Vieques is not expected to result in harmful health effects because (1) the estimated exposure doses from incidental ingestion for adults and children are below the conservative health guideline for adults and children and (2) the small amount of arsenic that can be absorbed through the skin is not likely to result in any serious internal effects.
• Exposure to iron in soil on Vieques is not expected to result in harmful health effects because (1) the estimated exposure dose from incidental ingestion for adults is below the conservative health guideline, (2) a child's estimated daily consumption is below levels known to result in childhood poisoning, and (3) only a minimal amount of iron is assumed to enter the body through the skin.
• Exposure to mercury in soil on Vieques is not expected to result in harmful health effects because (1) the estimated exposure doses from incidental ingestion for both adults and children are below levels of health concern documented in the toxicological literature and (2) the increased exposure expected to result from dermal contact is at least an order of magnitude lower than the reported NOAELs documented in the literature.