Atmospheric Environmenr Vol. 22. No. 2. pp. 429430. 1988. Printed in Great Britam.

0004-6981/88 S3.00+0.00 0 1988 Pergamon Journals Ltd.

AIRBORNE LEAD ON ST. THOMAS, U.S. VIRGIN ISLANDS

D. R. BROWN,* H. L. PACQUETTE and R. A. WATLINGTON

Division of Science and Mathematics, College of the Virgin Islands, St. Thomas, U.S.V.I. 00802, U.S.A.

(First received 8 December 1986 and infinalform 13 July 1987)

Abstract-Airborne Pb levels have been measured on St. Thomas, U.S.V.I., in locations that had previously been identitied, through Pb in roadside dust measurements, as potential sites of abundant environmental Pb. Airborne Pb levels have been found to follow similar trends to dust Pb levels. The average airborne Pb level in the busy urban area of Charlotte Amalie was found to be 0.39 pg rnm3,

Key word index: Lead, air, urban, automobile, U.S. Virgin Islands.

INTRODUCTION

Recently we reported the results of Pb analyses in roadside dust on St. Thomas, U.S.V.I. (Brown, 1986). We have now measured airborne Pb levels in many of the locations identified in the former study as potential sites of abundant environmental Pb.

We were originally concerned that the extreme proximity of houses, offices and schools to pasdng traffic in the urban area of Charlotte Amahe, St. Thomas, might result in significantly elevated Pb exposure to the occupants of these buildings, since previous workers have shown that in the vicinity of a busy road the environmental Pb levels rise dramatically within 5 m of the road (Harrison and Johnson, 1985; Rodtiguex-Flares and Rodriguez-Castellon, 1982). However, the dust Pb levels that we found were not as high as expected at these very short distances from the road. In the present study we have examined airborne Pb levels and their variation with distance of sampling site from the street, in order to verify our tentative conclusion based on Pb in dust measurements, that occupants of buildings within very short distances of the road in Charlotte Amalie are not subject to unacceptable environmental Pb levels.

In our roadside dust study we found the highest levels of Pb in sites on Mafolie Hill. This is the busiest of the hill roads leading out of Charlotte Amalie and the combination of high traffic volume and steep gradient undoubtedly gives rise to the elevated Pb levels in this location. Many houses and a school border this road so it was considered an important site for airborne Pb measurement.

EXPERIMENTAL

A General Mills High Volume air sampler was used. It was calibrated using the standard General Mills procedures. Samples were collected on Whatman High Purity Glass Microfiber filters. The instrument was fitted with a time switch. Samples were taken only during the hours 8 a.m. to 5 p.m. on weekdays between March and June 1986. Each sample was collected for 27 h. The sampler was free standing

* Present address: Department of Chemistry, University of Houston, Houston, TX 77004, U.S.A.

and the sampling height was approximately 1 m above street level.

Sampling sites on Main Street, Charlotte Amalie, were in a closed alley perpendicular to the street. The sampler was set up in the alley at 1, 8 and 15 m from the roadside. The sampling sites on Mafohe Hill were adjacent to the J. Antonio Jarvis elementary school. Two sites were used, one at 1 m from the road and a second at 8 m from the road adjacent to the school entrance.

Three separate sampling experiments were performed at each sampling site. Although no detailed record of meteoro- logical conditions on the sampling days was kept, all samples were taken on rain-free days when no more than very light winds were blowing.

The filter papers were digested in HCI using the standard Perkin Elmer method for Pb in air determination (Perkin Elmer Co., 1985). Lead concentrations were measured on a Perkin Elmer 2280 atomic absorption spectrophotometer, fitted with deuterium arc background correction, at the 283.3 nm Pb absorption line. Parallel digestions of blank filter papers were performed with each sample. Results are quoted as geometric means and standard deviations in pgrnm3 based on the measured volume of air through the sampler.

RESULTS AND DISCUSSION

The results are summarized in Table 1, where airborne Pb levels are compared with roadside dust Pb levels found in the same locations and Pb levels found elsewhere by other workers.

It can be seen from the results of sampling on Main Street, Charlotte Amahe, that the Pb levels in dust and air increase in roughly similar ways as the distance from the street decreases. A dramatic rise in Pb levels at very short distances is not observed, in either roadside dust or air. Even at only 1 m from the street Pb levels are no greater than average values found in typical urban locations in the U.S. and elsewhere, and the airborne Pb level is considerably below the EPA accepted maximum concentration of 1.5 pg rnv3 (U.S. Environmental Protection Agency, 1978).

We suggest that an explanation for the absence of a large increase in Pb levels on approaching within 5 m of the street may lie in the difference between the sites at which such a rise

429

430 Short C’ommunicatwns

Table I Pb concentrations in urban dust and air on St. Thomas. US. Virgin Islands and elsewhere

___~.. _._

Samphng site

Charlotte AmAe. St Thomas Mam Street. I m from road

8 m lrom road IS m lrom road

Malblie Hill. I m lrom road

8 m lrom road Kurd1 LocatIons. St. Thomas Urbana. Illinois b London. I! K ‘

Dust Pb cone Air Pb cone Ippm)’ (jig m ‘1’

800 550 460 ‘3WI

40 I OOu 3(K)- 3wo (IotlO common) xc Rural. U.K.

Typical, Urban. US ’ Central Antwerp’ Central Bombay. India” Central Lancaster. UKd

_

0.39 (0.04) 0.28 (0.02) 0.10(0.04) 4 3 (0.9) 0.85 (0.4) 0.02 (0.01)

0 13d 1-4 1 .o 0.350.65 3.8

a Geometric means and standard deviations. b Hopke et al.. 1980. ’ Millar and Cooney. 1Y83. I1 Harrison and Williams. IY82. ‘Smith. 1976. ’ De Jonghe and Adams. IY7Y. sKhandekar et al.. I984

has been observed, which have been adjacent to major highways away from city centres. and our sites in central Charlotte Amalie. In the former, overall emissions from fast moving traffic are probably higher. but are effectively dis- persed at all but the shortest distances from the road. In the latter sites, in confined streets. overall emissions may be lower but there is little breeze to disperse them resulting in a relatively gradual decrease in Pb levels on moving away from the street.

Airborne Pb levels on Mafohe Hill are again consistent with dust Pb levels, both of which were the highest recorded on the island. At 1 m from the road airborne Pb of 4.3 pg rn- ’ and dust Pb of 2300 ppm are high compared even to major urban centres. Generally airborne Pb levels > 1 pgm.-3 are considered to have significant effects on the blood Pb levels of those exposed to such air over extended periods (Waldron, 1975; Goldsmith, 1983). There are several h6uses on Mafolie Hill which are adjacent to the road with no intervening sidewalk, in which unacceptable airborne Pb levels may exist. particularly in rooms facing the street.

A second sampling site on Mafolie Hill was also chosen, 8 m from the road and at the entrance to the J. Antonio Jarvis elementary school. The airborne Pb level at this site was much reduced at 0.85 pg rnm3. Inside the school grounds we would anticipate lower Pb levels still and it seems unlikely that children at this school are exposed to unacceptable airborne Pb levels. Weconclude that, even though there are high levels ofemissions on Mafolie Hill because of the traffic volume and the steep gradient, its exposed nature ensures that the emissions are effectively dispersed by the wind at all but the shot-test distances from the road.

In conclusion, we have established that the local levels of Pb in roadside dust co&ate in a semiquantitative way with airborne Pb kvels measured at the same locations on St. Thomas. As might be expected. except in a few readily identifiable locations dust and airborne Pb levels are low compared to those found in urban centers elsewhere.

Acknowledgment-We gratefully acknowledge the National Institutes of Health who have supported this research through the MBRS programme.

REFERENCES

Brown D. R. (1986) Lead analysis in urban dust on St. Thomas. U.S. Virgin Islands. Armospkric Environment 20, 13051307.

De Jonghe W. and Adams F. (1979) The determination of organic and inorganic lead compounds in urban air by atomic absorption speztromctry with elsctrothcrmal atom- ization. Anal. Chim. Acre leS, 21-U).

Goldsmith J. R. (1983) Effect of airborne lead on blood lead. Atmospheric Ewironmenr 17,2X+2367.

Harrison R. M. and Johnaon W. R. (1985) Deposition fluxes of lead, cadmium, copper and polynucku aromatic hydro- carbons on the verges of a major highway. Sci. total Environ. 46, 121-135.

Harrison R. M. and Williams C. R. (1982) Airborne cadmium. lead and zinc at rural and urban sites in north-west England. Atmosplvric Enuir~nt 16.2669-2681.

Honke P. K.. Lomb R. L and Naturh D. F. S. (1980) h;lultiekm&tal charsEterization of urban roadway’ dust. Environ. Sci. Tech&. 14, 164-172.

Khandekar R. N.. Mishra U. C. and Vohra K. G. (1984) Environmental .kad exposure of an urban Indian PO& lation. Sci. total Envir&. 40.269-278.

Millar 1. B. and Coonev P. A. (1982) Urban lead-a study 01 environmental lead and its &n&nce to school chidren in the vicinity of a major trunk road. Atmospheric Environment 16, 61-20.

Perkin Elmer Co. (1985) Determination of lead in air by atomic absorption spectrometry.

Rodriuua-Flares M. and Rodtigucx-CastelIon E. (1982) IA and cadmium kveb in soil-id plants near highways and their cor&titxt with tnf& da&y. Environ. Poflut.. s&r. B. 4,281~290.

Smith W. H. (1976) Lead ccuttamin~ioa of the roadaide ecosystem. J. Air. Polk Gnstrol Ass. 21,75%766.

U.S. Environmental Pmtactioa My (1978) Q&y Assurance Hardbook of Air Pollution Meaweuunl Systemc, Vol. II, section 22.

Waldoa H. A. (1975) Lad kveb in &od of roai&nta near the M&A38 (M)in&&aa#c, w. Nature. Land. 253, 345-346.