Exposure to lead and an old way of counting.

We read with great interest the commentary by Jacobs et al. (2003) on the high cost of improper removal of lead-based paint and would like to address two issues, both related to the monitoring of lead-based paint. The first is the importance of animal sentinels and the second is the potential of the capture-recapture method (CRM) (also called the mark-recapture method) for determining the number of homes with lead-based paint.

The commentary by Jacobs et al. (2003) addresses issues and concerns related to cost when lead-based paint removal is performed improperly. The case study referenced by Jacobs et al. first arose from the discovery that the family pet, a dog, died from apparent lead poisoning. Discovery of lead poisoning through a family pet has been previously reported (Dowsett and Shannon 1994), and some have suggested that pets are good sentinels for poisoning of children (Berny et al. 1995).

A similar event took place in western Pennsylvania in the 1980s (Lange JH. Unpublished data): a homeowner reported that the family's dog was exhibiting unusual behavior. A veterinarian tested the dog and determined that it had lead poisoning. A water tower on property bordering the residence was being sandblasted and repainted, and sand had been distributed throughout the yard, with some inside the residence. The contractor had put a tarp barrier over the chain-linked fence as the only control measure to prevent spread of sand, dust, and lead-based paint. After the finding of lead poisoning in the dog, the single resident in this home was tested for blood lead; the resident also had lead poisoning (blood lead level by venous draw > 25 [micro]g/dL).

Most home and building owners are not aware of the hazards of lead-based paint nor its presence (Lange et al. 1998). Thus, it is common that renovation, repair, and/or demolition occur without implementation of lead-control or lead-safe practices (Lange et al. 1998; Lange and Thomulka 2000), with most never discovering the hazard or even being concerned (Lange et al. 1998).

Sentinel events identify potential areas of concern; however, they do not determine the magnitude of the problem. One of the difficulties in understanding the lead hazards is their magnitude (Jacobs et al. 2002). There is currently no good estimate for the number of homes having lead-based paint and the incidence find prevalence of lead-poisoned children and adults in most local areas. Accurate estimates of these parameters would better identify the extent of the problem in local communities. Why these estimates are not known is a result of the difficulty in collecting accurate data. However, a nontraditional environmental health method can be used for providing these estimates: the CRM (LaPorte et al. 1992; McCarty et al. 1993). The CRM has been used for decades by population ecologists and others who count wildlife (LaPorte et al. 1992). This method will allow sampling of the population, including homes with lead-based paint, to determine the incidence and prevalence at a fraction of traditional costs. To better identify the problems of lead, it is necessary to employ new and innovative methods such as the CRM.

With the CRM, population ecologists take a sample of fish, for example, from Lake Erie, and count them, tag them, and return them to the lake; then on the next day, they once again capture a sample of fish and identify the numbers of fish that were caught. Using a simple formula, such as the one presented, it is possible to estimate numbers of fish in the lake.

When estimating numbers of people with lead poisoning, we can use multiple sources of case ascertainment, including hospitals, laboratories, and schools. Each list represents a capture, and the duplicates on the lists represent the recaptures. We can use the same approach for estimating the number of houses with lead-based paint (i.e., the number of houses that might be contaminated). To do this, it would be necessary to obtain multiple incomplete listings of houses with lead-based paint from local agencies, the houses where lead poisoned children lived, surveys, and so on. The incomplete lists represent the captures, and the houses that appear on duplicate lists would represent the recaptures. Using a simple formula, we can obtain an estimate that controls for ascertainment.

N = (((M+1)(n+1)) / (m+1)) - 1,

where N is the estimate of number, M is the number marked in the first sample, n is the number collected in the second sample, and m is the number of those marked in the second sample that were collected.

Var(N) = ((M+1)(n+1)(M-m)(n-m)) / ([(m+1).sup.2](m+2))

95% confidence interval = [+ or -] 1.95 [square root of (Var(N))]

Because some of the houses could be false positives, a random sample of the houses could be tested. Then the estimated count could be adjusted to ensure accuracy of identification on the lists.

The animal reports demonstrate the importance of sentinels for detecting lead poisoning in people. The use of the CRM illustrates a more effective method for determining the number of people who experience lead poisoning and the number of homes that contain lead-based paint. Such information will allow a more accurate assessment of the problem and the financial resources needed for control.

The authors declare a real, apparent, or potential conflict of interest as defined in EHP's Instructions to Authors.

REFERENCES

Berny PJ, Cote LM, Buck WB. 1995. Can household pets be used as reliable monitors of lead exposure to humans? Sci Total Environ 172:163-173.

Dowsett R, Shannon M. 1994. Childhood plumbism identified after lead poisoning in household pets. N Engl J Med 331:1661-1662

Jacobs DE, Clickner RP, Zhou JY, Viet SM, Marker DA, Rogers JW, et al. 2002. The prevalence of lead-based paint hazards in U.S. housing. Environ Health Perspect 110:A599-A606.

Jacobs DE, Mielke H, Pavur N. 2003. The high cost of improper removal of lead-based paint from housing: a case report. Environ Health Perspect 111:185-186.

Lange JH, Bruce KM, Johnson RL, Phillips MJ, Smith DM, Weidenboerner KM. 1998. Survey of lead-based paint abatement projects in public buildings of Erie and Crawford Counties, Pennsylvania, USA. Regul Toxicol Pharmacol 28:73-78.

Lange JH, Thomulka KW. 2000. Evaluation of engineering controls for airborne lead exposure during renovation/ demolition of a commercial building. Indoor Built Environ 9:207-215.

LaPorte RE, McCarty DJ, Tull ES, Tajima N. 1992. County birds, bees and NCDs. Lancet 339:494-495.

McCarty DJ, Tull ES, Moy CS, Kwoh CK, LaPorte RE. 1993. Ascertainment corrected rates: applications of capture-recapture methods. Int J Epidemiol 22:559-565.

Editor's note: In accordance with journal policy, Jacobs et al. were asked whether they wanted to respond to this letter. They chose not to do so.

John H. Lange

Envirosafe Training and Consultants, Inc.

Pittsburgh, Pennsylvania 

E-mail [e-mail]

Ronald E. LaPorte

Graduate School of Public Health

University of Pittsburgh

Pittsburgh, Pennsylvania

Yue-Fang Chang

UPMC Presbyterian

Pittsburgh, Pennsylvania