Dust at Construction/Remediation Sites

Assessing the Risk

Dust inhalation as a health issue has received increasing scrutiny at construction and environmental remediation sites. Historically, the focus has been on inhalation of respirable particulates by workers, especially since instrumentation is readily available to provide real-time worksite data for particulates in air. However, the focus is now broadening to include health risks associated with contaminants contained in the airborne dust, and on more sensitive nearby receptors such as residences where dust may travel and settle. Dust-related risks thus vary as a function of two variables: dust concentration and contaminant concentrations in the dust.

Particulate Dust Inhalation

Health hazards associated with respirable dust as particulate matter include breathing difficulties such as asthma and chronic obstructive pulmonary disease (COPD), particularly in sensitive populations. In addition, breathing crystalline silica in dust can scar or damage lung tissue and can result in lung cancer or cardio-vascular and pulmonary diseases.

The Clean Air Act mandated the U.S. Environmental Protection Agency to develop National Ambient Air Quality Standards (NAAQS) for pollutants considered harmful to public health and the environment.  One such standard was developed for particulate matter less than 10 microns in diameter (“PM-10”). This standard is based on risk from dust as a particulate, independent of the presence of contaminants.

Field monitoring instruments are readily available that measure concentrations of PM-10 particulates in real time. These instruments typically include an alarm that can be set to activate at whatever particulate concentration the operator wishes to use, and/or notify the user remotely, if an unacceptable level of dust is being generated. Typically they are set to alarm when a particulate threshold, such as the NAAQS PM-10, is exceeded. Once it is known that a threshold has been exceeded, actions can be taken either to curtail the activity creating the dust, or to implement dust-control measures.

Contaminated Dust Risks

There has been increasing awareness that in addition to the hazards of airborne particulate matter, dust can contain contaminants that may pose significant health risks. In urban areas, soils often consist of historical fill that may contain metals, such as lead or arsenic, and organic compounds, such as polycyclic aromatic hydrocarbons (PAHs) and non-volatile petroleum hydrocarbons. Dust from these types of soils may represent a greater health risk due to the contamination they contain. Since there are no direct-reading monitors for these contaminants, dust meters can be used as a surrogate at construction and remediation sites. An increasing number of states require that dust monitoring take into account the type and amount of contaminant in dust, not just the presence of particulates. Greater emphasis has also been placed on potential risks to nearby residents, including children and passers-by.

Relating Particulate and Contaminant Risks

A paper prepared as an unofficial guideline by staff from the Massachusetts Department of Environmental Protection [http://www.mass.gov/eea/docs/dep/cleanup/laws/dustfin.pdf] provides a bridge between these two risk concerns – by providing graphs of contaminant concentrations in dust that represent a risk as a function of the particulate concentration. These graphs can be used to identify a particulate concentration at which a dust monitor alarm can be set to protect the specified receptor from the contaminant load in that dust. Although the graphs use very conservative assumptions about the length of time an individual may be exposed, and toxicity assumptions that may be unique to Massachusetts, the underlying calculations are also provided. A construction/ remediation site manager can substitute different assumptions into the calculations to derive graphs that are applicable to the site of concern.

Ultimately, much relies on monitoring methods in the field. Instrument calibration should be properly maintained, and monitoring at an upwind location is recommended to establish background dust levels that should not be included in risk calculations. Because wind direction will vary with weather, the upwind and downwind directions should be identified each day (at a minimum), and the monitors positioned as conditions dictate.

In order to properly utilize the graphs, the site manager must have reliable data for contaminant concentrations in site soil, which may be assumed to also be present in dust. In addition, ambient air will always have some concentration of background dust, so collecting background data before a project starts may be valuable. For long-term projects, actual analytical testing of dust may also be appropriate to demonstrate that the assumed contaminant concentrations were representative. Finally, care should be taken to ensure that contaminant toxicity assumptions supporting the graphs have not recently changed.

HETI…Helping Manage Risk

Hydro-Environmental Technologies, Inc. (HETI) offers a staff of experienced environmental and industrial hygiene professionals with proven capabilities to deal with a full range of risk control issues. We routinely provide air and dust monitoring services, as well as risk evaluation of contaminants at a wide range of sites and facilities. HETI has the experience and technical expertise to assist with hazard recognition, monitoring, and control to reduce the risk of dust exposure in the workplace.