Outreach Project: Heavy Metal Contamination at Urban Community Sites

The Jacobs Phytoremediation Collaborative

Aims: The goal of this outreach program is to provide expertise and assistance in assesing heavy metal contamination at public sites and community gardens. An example is provided here of in remediation of a brownfield site in Southeast San Diego. The site is an approximately 5,000 square feet triangle at the SW corner of the Jacobs Center for Neighborhood Innovation property. Chollas Creek runs along (and below) the North side. The South side is at the bottom of a hill on top of which sits the Guam Community (Figure 1). The site is located inside the Pueblo Watershed, which is the smallest and most polluted watershed in SD county. It is comprised of 60 square miles of predominantly urban landscape in San Diego that are drained by Chollas Creek, an urban coastal stream that emtpies into the San Diego Bay. As a result of urban runoff, Chollas Creek and the mouth of the creek in San Diego Bay is classified as "impaired" by the California State Water Resources Control Board. It contains hazardous levels of several metals inclusing copper, lead, and zinc. The Pueblo Watershed is home to 20 low-income neighborhoods, which are collectively referred to as Southeast San Diego (SESD). There are 591 vacant lots in SESD, many of which are Brownfield sites1.

Figure 1: Location of the brownfield site of interest in Southeast San Diego. The site is approximately 5,000 sq ft at an intermediate elevation relative to the surroundings, with Cholas Creek below and the Guam center on a hill above. The entire site was previously a military munitions plant that was decommissioned in the 1970's.




To evaluate the type and extent of contamination at the site, soil and plant tissue samples were collected. The initial plant tissue samples were collected and tested by Timothy O. Jobe, Qingqing Xie, Andrew Cooper in Julian Schroeder's Laboratory at UCSD and the soil samples were tested by Nicolas Lopez at SDSU Public Health laboratory. Several metal contaminants were found in the soil, including cadmium, arsenic, an cobalt. Similarly, high cadmium was found in the plant tissue samples (Figure 2).

Figure 2: Composite metal concentrations found in plant tissue collected from the proposed community garden site. While the concentrations of iron (Fe), manganese (Mn) and zinc (Zn) are within normal concentrations for plants, the cadmium (Cd) concentration is considerably higher than most foodstuffs, which generally contain less than 1 ppm.




Undergraduate students recieve training and pursue research projects aimed at testing and comparing the ability of different plant species to accumulate toxic metals. Students are being trained in presenting their research findings. Furthermore, we are recommending that the land owner implement a phytoremediation demonstration program at this site. This would be a set of side-by-side plots growing a combination of plants selected for the specific contaminants. Plant and soil samples would then be re-tested regularly and, based on test results, replanted with an optimized selection of plants.





WATER MONITORING OUTREACH PROGRAM

The Schroeder laboratory at UCSD began a collaboration with the San Diego Baykeeper organization ( www.sdbaykeeper.org) to assist the grassroots organization in monitoring water quality at sites throughout San Diego county. The San Diego Baykeeper was established to enforce the provisions of the federal Clean Water Act. The organization measures levels of bacteria and toxic metal contamination, and when contamination is found reports to governmental organizations (such as the EPA and the cities of San Diego and Encinitas). As some areas of the San Diego Bay are polluted, the work of the San Diego Baykeeper is instrumental in preserving the water quality in San Diego. The Schroeder lab has collected water samples from Paleta and Chollas Creeks, both designated toxic hot spots by the State Water Quality Board, and process these samples along with others collected from around the county. The water samples are being measured by ICP-AES analysis to determine the levels of dissolved metals and metalloids such as arsenic and lead. The data we are generating have been presented to the City of San Diego.



A brownfield is an abandoned or underused property previously used for industrial or commercial purposes and may be contaminated with hazardous substances. The environmental contamination may be real or perceived. Thus, brownfields have the potential to be returned to productive use once they have been evaluated for contamination and remediated if necessary.

According to the EPA, there are over 450,000 brownfield sites in the United States; however, there are many more undocumented brownfield sites. Remediating and rehabilitating these properties benefits communites by increasing local tax bases, facilitating job growth, and utilizing existing infrastructure, which reduces the need to develop open land and improves and protects the environment 1. Traditional approaches to remediate brownfield sites often involve physical removal of the contaminated soil and replacing it with uncontaminated fill dirt. Depending on the depth of contamination, a typical cost for this approach is approximately $50/sq ft. Because the average brownfield size is estimated to be over 6 acres (261360 sq ft.), this method can be cost prohibitive for many land owners. Therefore, the development of cost-effective alternative approaches has been a key goal in revitalizing brownfield sites.

One alternative approach called phytoremediation is a type of bioremediation that uses plants to remove or neutralize pollutants in the environment. Phytoremediation is especially useful for the remediation of toxic metals, inclusing cadmium, zinc, and nickel, as well as the metalloid arsenic. These potentially toxic substances are chemically analogous to the metals and metalloids plants need to survive. Some plants can naturally take up large amounts of these toxic metals and metalloids from the environment and store them in a manner that prevents toxicity to the plant. These plants are known as hyperaccumulators. Careful testing and planning is required for successful phytoremediation of a brownfield site as natural hyperaccumulators that are indigenous, or at least non-invasive, should be selected based on the location and climate of each site.









References:

1. http://www.theatlanticcities.com/politics/2013/03/how-congress-could-help-create-next-great-neighborhood/4893/

2. http://www.cadmium.org/pg_n.php?id_menu=6