Lihui (Michael) Huang
Environmental and Occupational Health Science Institute
University of Medicine and Dentistry of New Jersey-Rutgers University, New Brunswick
Hexavalent chromium (Cr-VI), one of the main forms of chromium (Cr) in ambient particulate matter (PM), is highly toxic and a well known human pulmonary carcinogen. It is also well known that Cr-VI species are usually present as both water-soluble and water-insoluble chromates in ambient air. The latter include, but not limited to, PbCrO4, BaCrO4 and CaCrO4. Both water-soluble and water-insoluble chromates are suspected respiratory carcinogens but possess different toxicity profiles. Many insoluble chromates have lower toxicity threshold limit values (TLVs) (10 µg/m3) than soluble counterparts (50µg/m3), which means higher toxicity and health risk caused by exposure to water-insoluble Cr-VI. Given the above, it is very critical to conduct separate measurements of water-soluble and water-insoluble Cr-VI in airborne PM. Recently, a reliable and sensitive measurement method for both soluble and insoluble ambient Cr-VI was developed by Dr. Fan’s group (Associate Professor in EOHSI, UMDNJ). Currently, the developed method is proposed to be applied for ambient Cr-VI measurement in locations with a variety of pollution sources.
While there are natural sources of chromium in the environment, most Cr-III and majority of Cr-VI originate from anthropogenic activities. The US EPA estimates that 64% of total atmospheric chromium results from the emission of hexavalent chromium from fossil fuel combustion and steel production, while 32% results from the release of trivalent chromium from chemical manufacture, chrome plating, cooling towers, and metal production. Obviously, the compositions of ambient chromium vary by the sources. Fuel combustion primarily discharges Cr-III into the environment as Cr2O3, with small amounts of Cr-VI. On the other hand, historical inappropriate disposal of industrial chromite ore processing residue in Hudson County, NJ may result in soluble Cr-VI as well as significantly higher level of insoluble Cr-VI in surrounding ambient air due to presence of water-insoluble by-products such as CaCrO4, calcium aluminochromate, tribasic calcium chromate, and basic ferric chromate. Accordingly, the ambient PM surrounding the contaminated sites is expected to contain a significantly higher ratio of insoluble Cr-VI substances than PM resulted from fuel combustion.
New Jersey Meadowlands is a general name for the large ecosystem of wetlands in northeast New Jersey in the United States. The Meadowlands, known for being the site of large landfills and decades of environmental abuse, consist of roughly 8,400 acres (34 km²) of open, undeveloped space in addition to developed areas that previously were part of the natural wetlands. The area includes a portion of Jersey City, where locates many historical chromite ore processing residue landfill waste sites (COPR). The re-suspension of Cr-enriched particulates in COPR may become an important source of ambient Cr in Meadowland area. In addition to COPR, other potential ambient Cr sources include, but not limited to, civilian waste landfill and fuel combustion (NJ Turnpike). Therefore, the concentration of ambient Cr-VI in NJ Meadowland, particularly insoluble Cr-VI, is expected to be significantly higher than other communities in New Jersey without identified Cr emission sources.
As part of ambient Cr-VI research activities in Dr. Fan’s group in EOHSI, ambient PM10 in Meadowlands will be collected by unique NaHCO3-pretreated MCE filters and Teflon filters. The former will be extracted by pH=4 HNO3 in 60ºC ultrasonic water bath for 40 min, and then the water-soluble Cr-VI in ambient PM will be speciated and determined by IC-ICPMS. Speciated Isotope Dilution Mass Spectrometry Method (SIDMS) with both 50Cr-III and 53Cr-VI spiking will be simultaneously employed to monitor the transformation of Cr species during sampling process. On the other hand, samples collected by Teflon filters will be digested by 2%NaOH-3%Na2CO3 (pH=12) under 95ºC microwave for 1 hr. The digested samples will be analyzed by IC-UV method to quantify total Cr-VI. The difference between the two types of samples indicates the level of insoluble ambient Cr-VI. As a result, the levels of ambient soluble and insoluble Cr-VI in Meadowlands will be obtained.
The results will benefit understanding health risks associated with exposure to ambient Cr-VI in communities within Meadowlands area. Through comparison to the data of Elizabeth, Rahway and Piscataway, the effects of Cr sources in Meadowland, i.e. COPR, landfill and fuel combustion, on the concentrations of ambient Cr-VI and ratios of insoluble Cr-VI to soluble fraction will also be examined and characterized.