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In summary, the Panel concludes that more data are needed for a full
assessment of health risk of potential exposure to the contaminants in Spring
I invite any questions you may have concerning the report or work of
Thanks again for the invitation to participate in this hearing.
GOVERNMENT OF THE DISTRICT OF COLUMBIA
MAYOR'S HEALTH POLICY COUNCIL
Anthony A. Williams
Bailus Walker, Jr., Ph.D., MPH
REPORT OF THE
REPORT OF THE
SCIENTIFIC ADVISORY PANEL
Under the provisions of Mayor's Order 2001-32 (March 1, 2001), the District of Columbia Mayor's Spring Valley Scientific Advisory Panel (the Panel) held its first advisory meeting on April 25, 2001. The meeting's agenda is attached along with a summary of the presentations to the Panel. The full text of the all presentations, including visual aids (slides, PowerPoint visuals) are available at the Office of the Panel's Executive Director located at 51 N Street, NE, 3rd Floor, Washington, DC 20001. Following the presentations and discussion among the presenters and Panel members, the Panel met in Executive Session (Panel members only). The Panel's conclusions and recommendations follow.
The District of Columbia's Department of Health should develop a comprehensive plan, the objective of which is to address concerns about the exposure to and the health effects of contaminants in the Spring Valley Community. This plan should delineate the roles and responsibilities of the multiple agencies involved in the project. For instance, the U.S. Army Corps of Engineers is pursuing work to determine potential exposure (soil sampling).
An appropriate reference frame for the plan is illustrated in the figure presented by Dr. Susan Metcalf of the Agency for Toxic Substances and Disease Registry (see attached). That figure is the "standard model" for relating environmental contamination with clinical disease. It is also found in numerous environmental medicine/health and/or toxicology textbooks and other related references.
Using that model, the District of Columbia's Department of Health along with its federal agency partners should determine how much, and what types of data are available or can be obtained for each entity or block in the model.
The Panel recognizes that it may not be practical to obtain all the data necessary to give precise answers to specific questions, which may be raised by the community members or other interested parties. For instance, assessing chemical mixtures. In reality, numerous chemicals are often present in environmental media such as soil or food resulting in concomitant exposure of humans either concurrently or sequentially to multiple chemicals. It is highly unlikely to be sufficient data for a precise or near-precise assessment of chemical mixture. There will be numerous other areas for which data are not available, and cannot be readily obtained. Indeed there is no “magic" in the scientific process, and science cannot give simple answers to complicated questions as quickly as may be desirable. The Panel is of the view that the agencies should clearly define in a coherent fashion, the minimum data set needed to draw reasonably sound conclusions about the environmental health conditions in Spring Valley, recognizing uncertainties often inherent in the scientific process.
Soil Sampling Analysis
The Panel recommends that the U.S. Army Corps of Engineers clearly articulate its strategy with respect to other contaminants – which contaminants may be present, and how these chemicals are being investigated. If it is established that the strategy is not comprehensive, the U.S. Army Corps of Engineers should develop another strategy based on further recommendation from the Panel.
The Panel is in general agreement with the soil sampling/testing plan proposed by the U.S. Army Corps of Engineers. Data obtained from this analytical process will provide information on “potential exposure” rather than “actual exposure" to the contaminants in the Spring Valley Community.
The Panel emphasizes that environmental measurements of air, water, soil or food represent potential exposures. Individuals residing in Spring Valley are likely to have significantly different actual exposures, depending on a number of factors such as occupation, proximity to the source of contamination, indoor pollution sources, and activity pattern (e.g., time spent indoors versus out). Therefore, although the potential for exposure may be the relatively similar, not all potentially exposed persons will experience the same actual exposure throughout in Spring Valley community. It is becoming increasingly apparent that a person's activity pattern is an important determinant of environmental exposure to most pollutants/contaminants.
The Panel recommends that the U.S. Army Corps of Engineers identify the chemical form or speciation of arsenic and other metals found in the soil analysis. Chemical form or speciation of the metal can be an important factor, not only for pulmonary and gastrointestinal absorption, but also in terms of distribution throughout the body and toxic effects.
Arsenic is particularly difficult to characterize as a single element because its chemistry is so complex, and there are many different arsenic compounds. It may be trivalent or pentavalent and is widely distributed in nature.
Airborne arsenic is largely trivalent, but deposition in airways and absorption from the lungs is dependent on the particle size and the chemical form. It has been known for some years that trivalent compounds of arsenic are the principal toxic forms.
The Panel recommends that the District of Columbia's Department of Health utilize the results of the U.S. Army Corps of Engineers proposed soil sampling as an indicator of places (neighborhoods within the Spring Valley Area) where additional biomonitoring should be implemented.
The Panel is fully aware that biomonitoring (hair analyses) has been conducted on a sample of the population at risk. But, the Panel believes that a "complete dataset" should include additional potentially at risk persons, specifically families or individuals residing in close proximity to the so-called “hot spots."
In biomonitoring it should be recognized that arsenic in hair may reflect past exposure, but intrinsic or systematically absorbed arsenic in hair should be distinguished from arsenic that is deposited from external sources, which may be difficult.
This recommendation for additional biomonitoring is not to suggest that every person in close proximity to a “hot spot" be monitored; rather a scientifically appropriate sample of the potentially exposed group should be selected for biomonitoring.
Cancer Registry Data
The Panel recommends that the District of Columbia's Department of Health select a different community or census tract for the purpose of comparing cancer incidence and mortality in the Spring Valley Community. The proximity (adjacent census tract) of the "case" to the control in the present Cancer Registry analyses makes it difficult to know whether the factor(s) determining the development of cancer is exposure to the soil contaminants being studied or another characteristic associated with living in the Spring Valley area or in the adjacent census tract. This is not to suggest that choosing the "right" control population would imply that the cancer differences are based only on exposure to arsenic.
In other words, it is not unreasonable to hypothesize that persons residing in the census tract that is adjacent to the Spring Valley area may have similar exposure to contaminants being studied. Therefore, the District of Columbia's Department of Health should select another "control population to ensure that the difference in potential exposure will likely constitute the critical difference and the absence or presence of cancer in this analyses), and is not likely to be attributable to differences in other factors (e.g., socioeconomic, etc.). The District should make sure to select a control population that is roughly matched with the case population (Spring Valley community) in age, race, and socioeconomic status.