The U.S. infrastructure needs top $2 trillion, according to the American Society of Civil Engineers.

Lead Exposure in Road Construction

Researchers' findings have confirmed there is increased risk for those who work on roads in highly populated areas.

There can be a substantial exposure to lead for workers who perform construction work on roadways. The lead has been deposited into the soil from years of using leaded compounds in gasoline. While the lead levels in air emissions have decreased dramatically since leaded gasoline has been banned from road usage, soil samples are still dangerously high in lead, especially in urban areas where vehicular traffic has historically been heavy.

At certain road construction sites, hazardous levels of lead could be present and air monitoring should be performed. Results might make it necessary for personnel to wearing protective respirators, which in turn would make medical surveillance necessary to ensure workers' blood lead levels are below the acceptable limits.

As the number of cars in the United States increased, so did lead emissions, increasing from 750 tons in 1928 to a peak of 2,250 tons in 1975 and then dropping to 750 tons in 1989. The drop in lead emissions starting in 1975 was caused by the federal law eliminating the use of leaded gasoline in on-road vehicles.

Mielke and Reagan examined data from soil samples taken from sites along U.S. roadsides and found inordinately high levels of lead residue. Their work was done in several locations to show consistent findings. Their premise is that leaded gasoline emissions would contain small particles of lead that would be deposited close to where it was emitted, along roadsides. "Given that gasoline lead produced 90% of U.S. air emissions in the 1970s and was, therefore, a major source of contamination in the environment, air inhalation and ingestion of street dust, house dust, and soil contamination by hand-to-mouth activity demonstrate that absorption from the lung and gut is biologically possible." (Mielke and Reagan, 1998) They found levels of lead in roadside soil samples were substantially higher than in other areas.

Laidlaw and Filippelli built upon the work of Mielke and Reagan, examining the correlation between the lead content in soils of urban roadways in Syracuse, N.Y., Indianapolis, and New Orleans and the content in soils of corresponding rural areas in the same states. Their findings confirmed increased risk for those who work on roads in highly populated areas. The same correlation was found of lead level present in relation to the nearness of the road; urban settings had much higher lead content than their rural counterparts, which is attributable to the higher volume of traffic in the urban settings. (Laidlaw and Filippelli, 2008)

In urban locations, the highest lead levels are above 900 ppm and are found in soil samples within 10 meters of the road center. This 10-meter range almost always includes the roadway shoulders. The shoulder is the area of most exposure to roadway workers because it is there that they access the road surface, and often this area is the part most disturbed by road work activities and equipment. Therefore, in this area of the roadway, workers are getting the maximum exposure to lead.

Although the soil levels of lead are generally stable until disturbed, typical actions done by road construction crews will cause the lead in the soil to become airborne in dust and particulate, which are the forms that are hazardous to humans.

Soil lead levels drop moving away from the road center. Forty meters away from the road center, levels are below 500 ppm in the soil. Again, a worker would not necessarily be exposed to this unless the soil is disturbed or dust is generated. Excavation, moisture of the soil, and weather conditions are factors in dust generation.

Job Site Exposure Controls
Lead is sequestered in blood, the soft tissues (organs, muscle and fat deposits), and in mineralizing tissues (bones and teeth) once it enters the bloodstream. The mineralizing tissues are where more than 95 percent of lead is stored in human bodies. Fortunately, lead stored in the bones and teeth is relatively stable and presents low toxicity to the individual. However, the other 5 percent of lead in the body can pose great danger.

Lead inhaled into the lungs is completely absorbed into the bloodstream. This is a significantly higher amount than that which is ingested. Ingested lead compounds are metabolized at only between 10 and 15 percent of the total ingested, although this can be as high as 50 percent for pregnant women and young children.

Even at the lowest levels found by Laidlaw and Filippelli, the levels are still above 100 ppm, and these are in rural areas. The lowest urban levels are still above 400 ppm. At those levels of lead present in the soil and in the form of lead chemical residue, that lead can readily be a risk to people near it if the soil becomes disturbed. (This finding assumes that the roadway of concern has been in existence since before 1975. Newer roadways would not be subject to the lead-depositing activity that Laidlaw and Filippelli sampled for. Air emissions fell from a relative peak of 220,000 tons of lead air emissions in 1970 to approaching zero tons in 1995. Rosen states that the average lead level in soil in the United States ranges between 7-20 ppm. (Rosen, 2002) This background lead level again is not usually leachable and thus presents low human toxicity risk.)

A September 1995 OSHA letter of interpretation from John B. Miles, Jr., director of the Directorate of Compliance Programs, concerned the need for an employee shower facility to decontaminate workers at an Ohio highway project. Sent to the president of an environmental service company, the letter said: "OSHA does not consider showers as feasible at every lead abatement construction site." OSHA cited the lead abatement standard: "The employer shall provide shower facilities, where feasible, for use by employees whose airborne exposure to lead is above the permissible exposure limit (PEL)."

Therefore according to OSHA, the responsibility lies with employers to ensure their workers are not being subjected to levels of lead above the PEL in performing their job duties and are not taking lead contamination off site after work is completed in their clothes, tools, or on their person. The PEL of lead is listed as a maximum of 50 micrograms per cubic meter of air. (29 CFR 1926.62(c)(1))

The construction lead standard describes what needs to be done to conduct an exposure assessment: "the employer shall collect personal samples representative of a full shift including at least one sample for each job classification in each work area either for each shift or for the shift with the highest exposure level." (1926.62.(d)(1)(iii)) The shower requirement, located in 1926(i)(3), calls for showers to be provided, where feasible. This section of the standard also describes eating facilities, hand washing facilities, and other methods of personal hygiene. It does not specify methods to achieve them, but rather gives the employer some latitude, as long as the employer provides adequate methods for the employee to remain safe from the lead exposure hazards.

The standard lists alternate methods of personal hygiene to help lower workers' exposure to lead on the job site -- methods that can be used in place of an on-site shower. They include using vacuums to remove dust and particulate from workers after work is concluded and providing protective outer clothing the worker can wear when on the site that would avoid possible lead dust/particles contamination with the worker's street clothing. The vacuums must be HEPA rated to protect the user and anyone nearby from the collected particles. The standard says employees with exposure above the PEL must have an opportunity to wash their hands "prior to eating, drinking, smoking or applying cosmetics. (1926.62(i)(4)(iii))

Air Monitoring
There is an imperative that employers must be monitoring airborne contamination their employees might be breathing while on the job. The letter of interpretation does not absolve the employer of this responsibility.

To ensure employees are not being exposed to levels above the PEL on the job site, monitoring is mandatory. Air sampling becomes the only conclusive method of determining whether employees are at or below the PEL. (1926.62(d)) Personal air sampling devices can measure the lead contamination in airborne dust that workers are breathing. Once established, this airborne lead level may fluctuate, depending on the activities being performed and the nearness of the worker to the most highly contaminated soil. This means levels need to be checked routinely.

In addition to monitoring the airborne concentration of the lead, the employer would be required to perform medical surveillance on workers to conform to the OSHA lead construction standard. (1926.62(j)) In performing this surveillance, the employer must ensure workers' blood serum level is below the OSHA level of 50 mcg/dl.

Data do indicate there is a definite need for concern, and the haunting prediction of Clair Patterson might be true: "Sometime in the near future it probably will be shown that the older urban areas of the United States have been rendered more or less uninhabitable by the millions of tons of poisonous industrial lead residues that have accumulated in cities during the past century." (Clair C. Patterson, National Academy of Sciences (1980)).

This paper mainly focused on leaded gasoline effects in the environment, but it needs to be mentioned that the trend from lead paint is steadily decreasing. From 1928 to 1989, it fell from about 1,250 tons to below one ton.

Summary of standards and regulations for lead

  • CDC, blood, 10 mcg/dL: Advisory; level of concern for children
  • OSHA, blood, 50 mcg/dL: Regulation; medical removal from exposure
  • OSHA, air, 50 mcg/m: regulation; PEL(***)(General industry)
  • OSHA, 30 mcg/m: action level
  • ACGIH, air, 150 mcg/m: Advisory; TLV/TWA(****) (under revision)
  • EPA, air, 1.5 mcg/m: Regulation; 3-month average
  • CDC (NIOSH), air, 100 mcg/m: REL(*****)
  • EPA, water, 15 mcg/L: Action level
  • FDA, food, 100 mcg/day: Advisory
  • CPSC, paint, 600 ppm (0.06%): Regulation; by dry weight

Data taken from CDC Case Study: Lead Toxicity

References
1. CDC Case Study: Lead Toxicity: http://wonder.cdc.gov/wonder/prevguid/p0000017/p0000017.asp
2. EPA Lead in Paint Dust and Soil: http://www.epa.gov/lead/
3. Laidlaw, M., Fillippelli, G., "Resuspension of Urban Soils as Persistent Sources of Lead Poisoning," Applied Geochemistry, 2008
4. Lewis, J. "A Historical Perspective on Lead," EPA Journal, May 1985: http://www.epa.gov/history/topics/perspect/lead.htm
5. Mielke, H., Reagan, P. "Soil is an Important Pathway to Human Lead Exposure," Environmental Health Perspectives, Vol. 106, Feb. 1998.
6. OSHA Construction Lead Standard: 29 CFR 1926.62
7. OSHA Interpretive Letter: http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=21914
8. OSHA Lead in Construction Guidelines: http://www.osha.gov/Publications/osha3142.pdf
9. Rosen, C., "Lead in the Home Garden and Urban Soil Environment," Minnesota University Agricultural Extension Service Publication, 2002.
10. Urban Lead Poisoning website: http://www.urbanleadpoisoning.com/

This article originally appeared in the March 2011 issue of Occupational Health & Safety.

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