Environmental Geochemistry and Health (1996), 18, 143 146

The relationship between surface dust lead Ioadings on carpets and the blood lead of young children

Scott Clark, Robert L. Bornschein, Winkey Pan, William Menrath, Sandy Roda and JoAnn Grote

Department of Environmental Health, PO Box 670056, University of Cincinnati, Cincinnati, OH 45267- 0056, USA

The final clean-up of residential lead abatement projects in federally-supported housing, as well as in other housing in a number of states, must meet surface dust lead clearance levels expressed as gg of lead per square foot. These clearance levels were established because hand-to-mouth ingestion of lead-contaminated dust is recognised as a major pathway through which many children are exposed. A dilemma exists because many floors in housing undergoing abatement are carpeted and the established clearance levels are generally not recommended for use on carpets. These clearance levels are also used as 'action levels' to determine whether exposure reduction activities are needed. The US Environmental Protection Agency is currently in the process of issuing standards for hazardous levels of lead in interior dust and bare soil under Title X of the Housing and Community Development Act of 1992, 'The Residential Lead-Based Paint Hazard Reduction Act of 1992'. An effort to develop a potential surface dust lead clearance level for carpets was made using an existing vacuum dust collection method that has previously been shown to be a reliable indicator of childhood lead exposure. This method was designed for use on carpeted and non-carpeted surfaces. Using data from the Cincinnati Soil Lead Abatement Demonstration Project, the suggested floor-dust lead level where an estimated 95% of the population of children would be expected to have blood lead values below the national goal of 10 gg dL -1, was more than an order of magnitude lower than the current floor-dust lead clearance level of 1080 gg m -2 (100 gg ft-2). Further comparisons of blood lead and carpet lead levels in other parts of the country should be performed before a risk-based lead loading clearance level is established.

Keywords: Blood lead, carpets, dust lead, lead standard, vacuum

Introduction

Carpeted areas in homes present a twofold chal- lenge to lead abatement: (1) the lead dust in carpets has been found to be difficult to remove (Clark et al., 1988; Ewers et al., 1994) and (2) there is currently no accepted method to determine if the carpets have been adequately cleaned. There is a need to know whether lead-contaminated dust in these carpets represents an important source of lead exposure for children living in these homes. Extensive vacuum cleaning of carpets from homes of families in older areas of Cincinnati has been found to remove an average of almost 300 mg m -2 Pb (27 900 gg Pbft 2) (Ewers et al., 1994). This level is 279 times the level of clearance dust lead that the US Department of Housing and Urban Develop- ment (HUD) (1995) has established for uncarpeted floors - 1080 ~tg m 2 (100 gg sq ft -2) that must not be exceeded following the clean-up of lead-based paint. The H U D surface-dust values are also used as 'action levels' in a risk-assessment protocol for public housing to determine whether immediate

0269-4042 �9 1996 Chapman & Hall

corrective action is needed to reduce childhood lead exposure (HUD, 1992). The samples for de- termining whether the level of floor dust lead meets the H U D clearance value are obtained by wipe collection of a measured surface area. This method has not usually been applied to carpeted areas because of the inherent difficulties in removing dust from carpets with a wipe. Thus, if carpet remains in a house after lead paint abatement has been completed there is currently no method to determine whether the abatement of lead in the carpets has been performed adequately.

One criterion in selecting the level of lead clearance, therefore, should be the level at which the blood lead level of an estimated 95% of the children exposed at that level will be below the limit specified as a national health goal, such as the 10 gg dL -1 estab- lished by the Center for Disease Control (CDC) as the level above which community intervention should be considered (CDC, 1991).

144 S. Clark et al.

Methods

An effort to develop a surface-dust lead clearance level for carpets was made using a standardised vacuum dust collection that was initially designed for use on carpets as well as on other surfaces (Que Hee et al., 1985). This method uses a personal air sampling pump as the vacuum source to collect surface dust f rom a measured area. Results using this method are expressed as both lead loading (lag m -2) and as concentrat ion (lag g-i). This collection method has been shown in a number of studies to produce dust-lead results that are correlated with the blood lead of children residing in the houses f rom which the samples were collected (Bornschein et al., 1985, 1987, 1991; Clark et al., 1991). In a number of these studies this method was used to collect composite surface dust samples f rom ap- proximately one square foot subareas in each of the following three rooms: the entry room of the hous- ing unit, the children's bedrooms and the room most often used by the child other than their bed- room.

Blood lead and carpet-dust lead data collected during the Cincinnati Soil Lead Abatement Demonstration Project (Clark et al., 1993) were available for analy- sis. The venous blood collected was analysed by anodic stripping voltametry (Roda et al., 1988). Dust samples were digested using hot nitric acid and were analysed by flame atomic absorption (Clark et al., 1993). The samples were collected before any dust or soil lead abatement conducted as part of the EPA-

supported Urban Soil Lead Abatement Project. Chil- dren were between 6 and 72 months old and only one child per household was used in the analyses. The data were analysed statistically by regression analysis and analysis of variance to determine the predicted carpet- dust lead levels where an estimated 5% of the blood- lead levels were above the values of 10 lag dL -1 and 15 lag dL -1.

The sources of lead in household dust have been found in previous studies (Bornschein et al., 1987; Clark et al., 1991) to be lead-based paint and exterior soil and dust contaminated by paint and other sources.

Water lead in the homes used in this study are low with a geometric mean of 1.9 lag L -1 for 30 min stagnation samples (EPA, 1991). Air lead values were less than 0.1 gg m -3 at the time of this study.

Results

Blood lead and carpet-surface lead data were avail- able from 23 homes where all three subareas were carpeted. The samples were collected in 1990 and the primarily 19th century housing units had pre- viously been rehabilitated, about two decades ear- lier, using procedures that resulted in the removal or enclosure of a very high proport ion of the lead- painted surface. The geometric mean blood-lead le- vel was 7.1 gg dL -1 and carpet surface dust lead le- vels were 66.9 gg mg -2 and 244 lag g 1 (Table 1). The blood level and dust level (lag m -2) data were statis- tically correlated (r = 0.52, p = 0.01) (Table 2).

Table 1 Statistical summary o f age, blood lead and carpet surface dust lead data (n = 23)

Geometric Geometric mean standard

deviation

Minimum Maximum 95%

Age (months) Blood lead (~tg dL 1) Carpet dust lead (gg g-l) Carpet dust lead (gg m -z)

26.4 1.8 7 63 57 7.1 1.9 1.8 20.8 15.2

244 2.6 15 1030 766 66.9 4.6 6.6 1733.3 125.0

Table 2 Results o f statistical analysis

(a) Intercorrelations between blood lead and dust lead

Ln dust lead loading Ln dust lead concentration

LnPbB 0.52* 0.27 0.01 ~ 0.21

Ln dust lead - 0.53 loading 0.01

(b) Analysis of Variance Ln blood = 1.091 + 0.2078 Ln dust lead loading (gg m -2)

(R 2 = 0.23, p = 0.01)

* Correlation coefficient. t p value.

Lead on carpets and blood lead of young children 145

In an effort to develop an exposure-related dust- clearance level, the dust-lead loadings were deter- mined for which an estimated five 5 % of the blood- lead values exceeded specified levels of 10 gg dL -1 and 15 lag dL -1. After the regression line of blood lead on dust-lead loading was established, a search was conducted for the dust-lead loading for which the 95 percentile of the predicted blood-lead value asso- ciated with it was 10 gg dL -1 (15 gg dL-1). Results from samples where all three subareas were carpeted revealed that at a surface dust-lead loading of 124 gg m -2 (11.5 gg ft -2) an estimated 5% of the blood lead levels are above 10 gg dL -1 and at 501 lag m 2 (46.6 lag ft -2) an estimated 5% of the blood-lead levels are predicted to be above 15 lag dL -1.

Discussion and Conclusions

Analysis of blood lead and dust-lead data from a mining community where dust lead was measured on hard-surface kitchen floors using the vacuum procedure described above and by using a wipe method, also led to the conclusion that the HUD clearance levels were much higher than levels where 95% of blood-lead values would be expected to be below 10 gg dL -1 (Clark et al., 1995). The dust-lead levels associated with this blood-lead level were 66 lag m -2 (6 gg ft -2) and 131 gg m -2 (12 gg ft -2) for the dust vacuum and wipe collection methods, respec- tively.

The dust collected by the vacuum procedure is repre- sentative of only the readily-available surface dust and is only a small fraction, on average about 1%, of the lead dust than can be removed with an industrial quality HEPA vacuum cleaner operating at a rate of 10 min per square metre of carpet (Ewers et al., 1994). Vacuum cleaning of the carpets for shorter times sometimes results in increased surface-dust levels (Clark et al., 1988; Ewers et al., 1994) and thus increased exposure. No relationship has been found between the amount of lead collected from the surface by the vacuum collection method and the total amount of removable lead dust in the carpet (Ewers et al., 1994). Because of the difficulty in removing lead dust from older carpets, the preferred action may be to remove the existing carpets.

If carpets are to be retained in the homes for economic reasons and/or because they are installed wall-to-wall in the homes, then a clearance level of 124 gg m -2

2 (11.5 gg ft- ), using vacuum dust sample collection, is suggested by these data to achieve only an estimated 5% of the blood-lead levels exceeding 10 gg dL -1. If the goal is to have only 5% of the blood-lead levels above 15 gg dL -1, then the suggested clearance level was estimated to be 501 gg m -2 (46 gg ft-2). Further comparison o f blood lead and carpet lead levels in other parts o f the country should be performed before a clearance level is established

Acknowledgements

Financial support for this work was in part from the Cincinnati Soil Lead Abatement Demonstra- tion Project, EPA V00503501 and Ohio Depart- ment of Health - Center for Disease Control Grant 731-C, but does not represent the views of these agencies. Deling Niu contributed to the statistical analyses.

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[Manuscript No. 352: received July 1, 1994 and accepted after revision on November 1, 1995.]