Blood Lead Levels and Remediation of an Abandoned Smelter Site

Article excerpt

Numerous studies have examined the health effects of lead exposure and have documented adverse health effects for a range of exposure levels (1-20). Several studies have documented positive associations between blood lead levels and soil or household dust levels (21-25). However, few published studies have examined blood lead levels in communities with an inactive smelter contaminated with mining and smelting wastes (22,26-29). Health concerns have been associated with soil lead levels above 150-500 ppm (20).

In 1989, lead levels as high as 1,520 micrograms per gram (parts per million, ppm) were identified in residential soil samples 300 feet from an inactive lead/zinc smelter site in Socorro, New Mexico, (population 8,159: 1990 census). The smelter had been in operation from 1883 to 1894. A slag pile coveting 500,000 square feet remains, with lead concentrations up to 24,800 ppm in the pile. Homes are located as close as 20 feet to the pile. Access to the pile was not restricted by fencing until 1990.

Removal actions were conducted by the U.S. Environmental Protection Agency (EPA) between August 15, 1990, and January 9, 1991. Contaminated soil and slag from the residential areas were consolidated on the smelter property and covered with a cap of clay and fill dirt. A fence was built around the area, and warning signs were posted.

This study, conducted by the New Mexico Department of Health (NMDOH) and funded by the Agency for Toxic Substances and Disease Registry (ATSDR), compares the pre- and post-cleanup blood lead levels of the residents living near the site. In addition, blood lead levels of residents near the site were compared to blood lead levels of other community residents. Associations for other risk factors, such as occupational exposure, and elevated blood lead levels were also examined.

Methods

Selection and definition of study areas

The community of Socorro, New Mexico, was divided into three study areas: 1) the smelter area, 2) the northeast area, and 3) the town area. The smelter area was defined as the 63 properties identified by the EPA in 1990 as having soil lead levels above 500 ppm. Thirty-two of these properties were within 1/4 mile of the center of the slag pile, with the remainder properties within 1/2 mile. Residences were located on 37 of the properties. None of the streets in the smelter area were paved at the time of the study.

A neighborhood located on the opposite side of the community, two miles northeast of the smelter, was selected as one comparison site, the northeast area. There was no historical evidence that this area would have elevated soil lead levels due to mining, milling, or smelter activities, although wind could have blown smelter contamination in that direction. The northeast neighborhood is similar to the smelter neighborhood in its diverse mix of home types on varying lot sizes. Some roads in this area were unpaved.

The third area, the town area, included residents who participated in the study because of concern about lead, but did not live in the smelter or northeast areas. Most were within 1/2 mile of the smelter. Eleven homes were over one mile from the smelter.

Collection of blood samples

On July 31 and August 1, 1990, a lead screening clinic was offered by NMDOH at the community health office in Socorro, located in the town area. Residents were invited to the clinic through a public notice in the local newspaper, a mailing of individual letters, and door-to-door, in-person visits. In October 1991, a second screening clinic was offered using the same notification methods to those who had participated in the first clinic and any other interested residents of the areas. The methods and contract laboratory (a nationally-recognized, certified laboratory, recommended by the Centers for Disease Control and Prevention) were the same as those used for the first screening. The detection limit for blood lead was 5 ug/dl. …