ENVIRONMENTAL SCIENCE AND TECHNOLOGY BRIEFS FOR CITIZENS
by M. Lambert, B.A. Leven, and R.M. Green New Methods of Cleaning Up Heavy Metal in Soils and Water Innovative solutions to an environmental problem This publication is published by the Hazard- ous Substance Research Centers as part of There are several options for treating Joplin. Here, mine spoils (locally called their Technical Outreach Services for Com- or cleaning up soils contaminated with chat) cover much of the open space in- munities (TOSC) program series of Environ- heavy metals. This paper discusses side the city, and contain high levels of mental Science and Technology Briefs for three of those methods. lead, zinc, and cadmium. Heavy metal Citizens. If you would like more information about the TOSC program, contact your re- contamination can be carried with soil gional coordinator: Introduction particles swept away from the initial At many sites around the nation, heavy areas of pollution by wind and rain. Northeast HSRC metals have been mined, smelted, or Once these soil particles have settled, New Jersy Institute of Technology Otto H. York CEES used in other industrial processes. The the heavy metals may spread into the 138 Warren St. waste (tailings, smelter slag, etc.) has surroundings, polluting new areas. Newark, NJ 07102 sometimes been left behind to pollute Cleanup (or remediation) technologies (201) 596-5846 surface and ground water. The heavy available for reducing the harmful ef- Great Plains/Rocky Mountain HSRC metals most frequently encountered in fects at heavy metal-contaminated sites Kansas State University this waste include arsenic, cadmium, include excavation (physical removal of 101 Ward Hall chromium, copper, lead, nickel, and the contaminated material), stabiliza- Manhattan, KS 66506 zinc, all of which pose risks for human tion of the metals in the soil on site, (800) 798-7796 health and the environment. They typi- and the use of growing plants to stop Great Lakes/Mid-Atlantic HSRC cally are spread out over former indus- the spread of contamination or to ex- A-124 Research Complex-Engineering trial sites and may cover acres of land. tract the metals from the soil Michigan State University Figure 1 shows one such site in south- (phytoremediation). East Lansing, MI 48824 (800) 490-3890 western Missouri, near the city of
South/Southwest HSRC Environmental Science & Technology Program Georgia Tech Research Institute 229 Baker Building Atlanta, GA 30332 (404) 894-7428
Western Region HSRC Oregon State University 210 Strand Agriculture Hall Corvallis, OR 97331-2302 (800) 653-6110
Acknowledgment: Although this article has been funded in part by the U.S. Environmen- tal Protection Agency under assistance agree- ment R-819653, through the Great Plains/ Rocky Mountain Hazardous Substance Re- search Center, it has not been subjected to the agencys peer and administrative review Figure 1. Mine spoils called chat, near the city of Joplin, Missouri. and, therefore, may not reflect the views of Wind and rain can cause the chat to scatter, spreading heavy metal the agency. No official endorsement should contamination. be inferred. ENVIRONMENTAL SCIENCE AND TECHNOLOGY BRIEFS FOR CITIZENS PAGE 2
Excavation Table 1. Comparative costs for different types of heavy metal soil remediation Excavation and physical removal of the (Schnoor, 1997). soil is perhaps the oldest remediation TrnoitaidemeRfoepy Cdetemcibuc/tso eriuqeRemiT method for contaminated soil. It is still in use at many locations, including resi- E0lavomerdnanoitavacx $s04$-001 htnom9-6 dential areas contaminated with lead utisnI noitaxif $s002$-09 htnom9-6 in southwestern Missouri. Advantages )stnemdnemaliosgnidulcni( of excavation include the complete re- moval of the contaminants and the rela- P0noitcartxeotyh $s4$-51 htnom06-81 tively rapid cleanup of a contaminated site (Wood, 1997). Disadvantages in- ity of heavy metals on site has many lead. Chemical reactions between the clude the fact that the contaminants advantages over excavation. One way phosphate and the lead cause a min- are simply moved to a different place, of stabilizing heavy metals consists of eral to form called lead pyromorphite. where they must be monitored; the risk adding chemicals to the soil that cause Lead pyromorphite and similar miner- of spreading contaminated soil and dust the formation of minerals that contain als called heavy metal phosphates are particles during removal and transport the heavy metals in a form that is not extremely insoluble. This means the of contaminated soil; and the relatively easily absorbed by plants, animals, or new minerals cannot dissolve easily in high cost. Excavation can be the most people. This method is called in situ (in water (Lambert et al., 1997). This has expensive option when large amounts place) fixation or stablization. This two beneficial effects. The minerals of soil must be removed or disposal as process does not disrupt the environ- (and the heavy metals) cannot be eas- hazardous or toxic waste is required ment or generate hazardous wastes. ily spread by water to pollute streams, (see Table 1). Instead, the heavy metal combines with lakes, or other groundwater. Also the the added chemical to create a less toxic heavy metal phosphates are less likely Stabilizing Metals in compound. The heavy metal remains to enter the food chain by being ab- the Soil in the soil, but in a form that is much sorbed into plants or animals that may Heavy metals can be left on site and less harmful. eat soil particles. Table 1 shows the cost treated in a way that reduces or elimi- of treating the soil by in situ fixation nates their ability toadversely effect One example of in situ fixation of heavy may be about half the cost of excava- human health and the environment. metals involves adding phosphate fer- tion and disposal of heavy metal con- This process is sometimes called stabi- tilizer as a soil amendment to soil that taminated soil. This method is rela- lization. Eliminating the bioavailabil- has high amounts of the heavy metal tively rapid and takes about the same amount of time as excavation. Use of Plants Growing plants can help contain or re- duce heavy metal pollution. This is of- ten called phytoremediation (EPA, 1988). It has the advantage of relatively low cost and wide public acceptance (Schnoor, 1997). It can be less than a quarter of the cost of excavation or in situ fixation. Phytoremediation has the disadvantage of taking longer to accom- plish than other treatment . Plants can be used in different ways. Sometimes a contaminated site is simply reveg- etated in a process called phytostabilization. The plants are used to reduce wind and water erosion that spread materials containing heavy metals. In one example, grass or tree buffers could reduce sediment loss from Figure 2. Test plots for evaluating revegetation of chat material in Galena, the chat piles at a contaminated site in Kansas. Here, tall fescue is being grown as a way of reducing sediment runoff Galena, Kansas, anywhere from 18% and the spread of heavy metal pollution. The bare center plot is a control in to 25% (Green, et al. 1997). If all of the which fescue was not planted. ground could be revegetated, sediment ENVIRONMENTAL SCIENCE AND TECHNOLOGY BRIEFS FOR CITIZENS Page 3 loss could be cut by approximately 70%. Conclusions sis Center Technology Evaluation However, it would be necessary to find During the 1990s, new methods have Report TE-98-01, 37. plants that could tolerate high levels of been developed to clean up heavy metal- heavy metals. Figure 2 shows a series contaminated soil. The expensive pro- Wood, P., 1997, Remediation Methods of several revegetation test plots on the cess of excavating and disposing con- for Contaminated Sites: in R. chat piles in Galena, Kansas. taminated soil has been augmented with Hester and R. Harrison, Contami- new methods that treat the soil in place. nated Land and Its Reclamation, Another way plants can be used to clean In situ fixation is a process that cre- the Royal Society of Chemistry, up heavy-metal contaminated soil is ates new chemical coumpounds in Cambridge, p. 47 71. called phytoextraction. Some plant spe- which heavy metals are much less cies can take up heavy metals and con- available to living things. This on-site U.S. Environmental Protection centrate them in their tissue. The cleanup is less disruptive to peoples Agency (US EPA), 1998, A Citizens plants can be harvested and the con- lives and to the environment compared Guide to Phytoremediation, Office taminated plant material disposed of to excavating and disposing contami- of Solid Waste and Emergency safely. Sometimes soil amendments are nated soils elsewhere. Phytoreme- Response (5102G) EPA 542-F-98- added to the soil to increase the ability diation uses plants by several methods 001 August 1998. of the plants to take up the heavy met- to contain or clean up heavy metals. als. One type of plant used for this Phytoremediation has the benefit of be- US EPA, 2000, Introduction to purpose is called Indian mustard. This ing a relatively low-cost, natural solu- Phytoremediation, National Risk plant has been used to extract lead from tion to an environmental problem. Management Research Laboratory, soil and reduce lead contamination at Office of Research and Develop- various contaminated sites. Other More information on these and other ment, EPA/600/R-99/107, February plants that may be used for new cleanup methods for contaminated 2000. phytoextraction include alfalfa, cab- soils and water is on the internet at bage, tall fescue, juniper, and poplar many sites, including
Great Plains/Rocky Mountain HSRC Kansas State University 101 Ward Hall Manhattan, KS 66506 (800) 798-7796