Remediation of heavy metal soil contamination: Developments in Japan
Nikko, the UNESCO World Heritage site, is one of the most popular tourist attractions in Japan. One tourism site writes: “The view (from nearby Mt Nantai) is breathtaking, as if you are in paradise1.” Unbeknown to most tourists, just over the mountain ridge to the south of Lake Chuzenji is another view – the 3000-hectare moonscape that was once the Ashio copper mine2, and downstream in the Watarase River Basin, 100,000 hectares of once-polluted farmland3.
Metal mining in Japan has a long history. Between 1540 and 1640, when prices collapsed, Japan produced up to half as much silver as did all of Spanish America. In the late 17th century, Japan produced twice as much copper as Sweden, then the most important source of copper within Europe4, with up to 1,500 tons annually from the Ashio mine5. Between 1610 and 1973, the Ashio mine produced 700,000 tons of copper. A 1956 census listed 1,404 abandoned metals mines6. The struggle with heavy metal pollution continued with mercury pollution in Kyushu and cadmium pollution along the Jinzu River valley. In the Jinzu River valley alone, more than 1,500 ha of paddy land were contaminated7.
Japan still endears chronic background heavy metal pollution. In spite of having no upstream mines or industrial sites, some rice paddy areas in Japan nevertheless suffer from natural geological heavy metal contamination. Most of the pre-modern abandoned mines remain untouched and an unknown number continue to seep.
This article focuses on rice paddy remediation. CODEX and the status of rice in Asia are pressing for the removal of contaminants from the soil itself, not just from the rice. From April 1, 2010, new regulations in Japan prohibit swapping good soil for bad; remediation must be of the soil already in place.
Beside regulation, the high costs of mechanical soil replacement, such as soil dressing methods, make them uneconomical for agricultural land. Of course, heavy metal pollution is not limited to Japan. Heavy metal contamination afflicts more than 300 ha of Taiwan’s rice paddies8.
Rice paddy soil contamination
Rice paddy soils present both unique opportunities and restrictions for remediation. The goal of maintaining them or returning them to productive agriculture rules out some technologies such as pyrometallurgical separation.
In addition to natural geological heavy metal contamination, annual flooding of the paddies can replenish contaminants, forcing remediation to be repeated periodically. For example, 10 ppb cadmium in irrigation water containing can lead to 1 ppm Cd in soil, because essentially all Cd in the water accumulates in the soil. Avoiding Cd recontamination requires less than 1 ppb in irrigation water7.
On the other hand, the flooding stage of rice growing presents opportunities for lengthy aqueous treatments including some of the newer competitive treatments discussed below.
Perhaps the oldest remediation technology, soil dressing, involves capping the contaminated soil with an impermeable layer of hard packed soil, followed by a topping of uncontaminated soil transported from another soil. If these two layers are simply placed on top of existing soil, the topology of the entire area must be raised as a unit, including roads and irrigation canals. Alternatively, but more expensively, the contaminated soil can be temporarily removed, trenches dug in the subsoil and the contaminated soil buried in the trenches. This trench system is then capped and a topped with good soil7.
Soil dressing is an expensive excavation technique and usable uncontaminated soil is becoming harder to find9. Also, after 30 years of using this method Japanese localities are finding recontamination of some top soils due to irrigation and rainfall7.
Ex situ heavy metal extraction
Dowa Eco-System Co, Ltd operates ex situ soil washing services at its Hanaoka plant in northern Japan10. The largest operation of its type in Japan, and with a capacity of 50,000 tons per month, the Hanaoka plant combines mechanical washing, classification, magnetic separation, flotation and extraction. Cleansed soils are then returned to their original sites.
Although ex situ remediation is currently viewed as a permanent remedy11, the findings of recontamination for sites treated by soil dressing7 raises questions about true permanency. In addition, contaminated rice-paddy soils are found throughout Japan. Contaminant levels are relatively low but still too high to yield CODEX-compliant rice12. Excavation and transportation costs make ex situ remediation too expensive for most rice paddy soils.
In situ immobilisation
Toda Kogyo Corporation markets a series of inorganic oxide powders modified with magnesium, calcium, aluminium and/or iron13. Their current line of powders, also marketed by spin-off Fujikasui Engineering Co, Ltd, is designed to form insoluble complexes with As, Pb, Cd, Hg, Se, Cr6+, F and B. In practise, for example, powder AMH-1200 is mixed 150 kg per cubic meter of soil to reduce Cd from 0.067 mg/L to less than 0.005 mg/L.
Hiroshi Hasegawa at Kanagawa University developed two lines of immobilisation adsorbents for heavy metal contaminated soil. The first is marketed by Pure Techno (Maebashi, Gumma) under the trade name ZeoForce 583. Literature about this product is sparse but company’s web site claims 100% removal of hexavalent chromium, cadmium, arsenic and selenium with greater than 90% removal of lead, fluorine and boron14.
The second product is marketed by Technica LLC (Kobe) under the trade name TG Catch II15. A synthetic zeolite, this white powder is marketed as a means to reduce hexavalent chromium, cadmium, arsenic, selenium, lead, fluorine and boron to below regulatory limits.
Taiheiyo Cement also markets an immobilisation under the trade name DENITE.16 DENITE functions by forming insoluble hydroxides at about pH 10.
Taiheiyo Cement and the Nagano Agricultural Research Center jointly developed a ferric chloride soil flush16. In this process17, the patch of soil to be treated is first isolated with a perimeter barrier. The isolated soil is then flushed with a ferric chloride solution at a pH between 2 and 3. The collected ferric chloride solution and first water flush are processed at a plant to remove contaminants. The soil is then flushed twice more with water. The Ministry of Agriculture, Forestry and Fisheries (MAFF) currently advocates this method18.
Fe-Cat™ catalytic iron remediation
Much heavy metal ‘cancer’ has been removed from Japanese agricultural soil. Nonetheless, persistent levels of natural groundwater contamination and irrigation water contamination make for chronic contamination that needs to be treated on an ‘out-patient’ basis, non-surgically if possible. Soil dressing and soil washing, while suitable for acute contamination requiring major surgery, are simply too expensive for chronic contamination.
Motivated by the need for less expensive and simpler treatments for chronic soil contamination, CORDA LLC, in cooperation with the University of Tsukuba and Kobe Steel, set out to develop do-it-yourself technology that can be placed inexpensively in the hands of farmers.
Because of its low cost and ready availability, CORDA focused its attention on commercially available iron sintering powders. Zero-valent iron (ZVI) catalytically decomposes organic contaminants and is widely used for that purpose. In spite of the history of iron cementation in precipitating copper from mining waste water, iron powder was impractical for heavy metal contamination. Under acidic conditions, deposition and hydroxide formation inactivate the iron surfaces; under alkaline conditions, ferrous to ferric oxidation increases and necessitates strong agitation. So when used for waste water streams, iron powders require concentration adjustments that are impractical for soil remediation9.
When applied to dilute aqueous conditions, the surfaces of most iron powders ionised to only a very limited degree and cannot be used for heavy metal immobilisation. For this reason, development to date focused on iron salts, mainly sulphate and chloride, and ferric chloride soil flushing, MAFF’s current recommendation. However, ferric salts leave behind anionic residues that require further water washes and treatment of the resulting waste water.
Researchers at CORDA and the University of Tsukuba recently discovered that certain water atomised iron powders, which are commercially available sintering powders, have highly catalytically reactive surfaces, and that these inexpensive iron powders immobilise cadmium and lead in amounts that greatly exceed those for conventional iron powder. The surfaces of these powders catalytically maintain their iron ionisation activity and enable immobilisation of heavy metals without resorting to ferric salts9. These surfaces resist poisoning and maintain full activity in the presence of EDTA (Ethylenediaminetetraacetic acid).
Laboratory tests using 1 wt% Fe-Cat iron powder in pH 7 aqueous solutions reduced the concentration of cadmium from 5 ppm to less than 0.01 ppm in 48 hours. This reduction took place both in the presence and absence of EDTA. Laboratory tests using contaminated soil samples from rice paddies gave similar results. Because EDTA persists in the environment and is likely to be banned, as it is in Europe, one focus of laboratory research is one more environmentally acceptable, chelating agents. Other laboratory research focuses on variations among types of soils.
Field tests in rice paddies are currently underway. Using conventional fertiliser spreading equipment, Fe-Cat iron powder was spread on the paddy one week before seedling transplantation, and worked into the soil to a depth of 30 cm. A 20-a plot was divided into three subplots, which were treated respectively with 1 wt% (1 ton), 0.5 wt% (0.5 ton) and no iron powder. The photographs show spreading with a backpack spreader – a wagon spreader could not get into the field due to recent rainfall.
If successful, this paddy will yield CODEX-compliant rice at the same time as it is being treated. In other words, from a farmer’s perspective Fe-Cat iron powder can be viewed as a form of fertiliser, or other soil amendment. The cost for treating a paddy contaminated with 1 ppm cadmium is estimated to be about 2 million yen (~ $23,000) per hectare; existing government subsidies to farmers could bring the cost to the farmer to a fourth of that. If current tests are successful, commercial use could begin as early as the 2011 growing season.
While Mulligan’s comparison of costs is widely cited19, more recent compilations are available in the FRTR Remediation Technologies Screening Matrix and Reference Guide, Version 4.0. Representative costs for selected technologies are shown in the table. The FRTR gives costs in terms of volume of soil, so these were converted to area costs assuming treatment of the top 30 cm of soil.
A common treatment trajectory in medicine is for invasive procedures that require lengthy hospitalisation to be gradually replaced by less invasive, less drastic treatments, and these are then gradually replaced by out-patient and in-home treatments. Soil remediation technologies are following a similar trajectory. The surgical soil dressing technologies of the 1970s handled the most serious treatable soils. The trend from here forward will be to treat chronically reoccurring contamination using inexpensive methods that farmers can implement.
CORDA LLC is an environmental consultancy located in Tsukuba, Japan. Contact: [email protected]
TT Crossroads is a technology transfer consultancy located in Tsukuba, Japan. Contact: [email protected]
1 http://www.nikko-jp.org/english/sekaiisan/index.html; http://famouswonders.com/nikko-national-park/ 2 Ashio copper mine: http://maps.google.com/maps?q=36.683013,+139.432640; Lake Chuzenji: http://maps.google.com/maps?q=36.735995,+139.475555 3 Ui, Jun, ed., Industrial Pollution in Japan, United Nations University Press, 1992, http://d-arch.ide.go.jp/je_archive/society/book_jes5_a.html; Pawitan, Hidayat et al., Catalogue of Rivers for Southeast Asia and the Pacific, Vol. III, http://flood.dpri.kyoto-u.ac.jp/ihp_rsc/riverCatalogue/Vol_03/index.html 4 Flynn, D.O., Giraldez, A http://mauricio.econ.ubc.ca/pdfs/flynn.pdf (2003) 5 Koide, Goro Chemistry & Chemical Industry, Vol.63, 7 July 2010, p.589 (http://www.chemistry.or.jp/kaimu/ronsetsu/ronsetsu1007-e.pdf) 6 Sakamaki, Yukio et al Chishitsu News, Sept 1979, No. 301, pp.40-51 (http://www.gsj.jp/Pub/News/pdf/1979/09/79_09_06.pdf) 7 Yamada, Nobuaki Japanese Journal of Soil Science and Plant Nutrition 78:4 (2007) 411-416 8 Hseu, Zeng-Yei, Chen, Zueng-Sang, Jien, Shih-Hao JIFS 4 (2007) 35-58 9 Fukushima, Hisayo “Investigation of cadmium removal processes in rice paddies using iron particles,” Masters Dissertation, Univ Tsukuba, January 2010. 10 http://www.dowa-geo.jp/service/pu_wash.html 11 Shiratori, Toshikazu Shigen-to-Sozai, 119:8 (2003) 441-450 12 Makino, Tomoyuki et al Environmental Pollution, 144:1 (2006) 2-10 13 http://www.todakogyo.co.jp/docs/products/function/amh/amh.pdf 14 http://puretechno.eco.coocan.jp/newpage15.html 15 http://www.technica-goudou.co.jp/pdf/tg_catch2_studies.pdf; http://www.technica-goudou.co.jp/pdf/tg_catch2.pdf 16 http://www.taiheiyo-cement.co.jp/service_product/denite/pdf/catalog.pdf 16 http://www.niaes.affrc.go.jp/magazine/pdf/seika06_48.pdf 17 Makino, Tomoyuki et al Japanese Journal of Soil Science and Plant Nutrition 79:1 (2008) 101-107 18 http://www.affrc.go.jp/ja/news_event/press/2005/050701 19 Mulligan, C.N., Yong, R.N., Gibbs, B.F. Engineering Geology 60 (2001) 193-207
Masaru SAKAI Founder of CORDA LLC, an environmental consultancy based in Tsukuba, Japan, and inventor of Fe-CatTM soil rescue technologies, Mr Sakai specialises in assembling and operating the complex ties between corporate funder, university laboratory, agricultural cooperative and local government needed to solve environmental problems.
Hisayo FUKUSHIMA As a masters student at the University of Tsukuba, Ms Fukushima conducted the basic studies needed to establish Fe-Cat(tm) as a viable and competitive candidate for low cost remediation of heavy metal pollution in soil. Ms Fukushima is currently a researcher at the National Institute for Agro-Environmental Studies.
Kiyoharu NAKATANI, PhD Associate professor of chemistry at the University of Tsukuba, Dr Nakatani has researched particle chemistry and physics since his days as a researcher at Fuji Photo Film in the late 1980s. A JST ERATO scientist 1990-1993, Dr Nakatani’s recent focus includes basic research on single particles and single oil microdroplets, in order to better understand their adsorption to and desorption from soil, and uptake by biological organisms. Dr Nakatani received his PhD from Osaka University.
Alan ENGEL, PhD Founder of TT Crossroads, a technology transfer consultancy based in Tsukuba, Japan, Dr Engel combines intellectual property analytics, business strategy and public relations to help universities improve their patent portfolios and create industrial collaborations. A JST ERATO scientist 1984-1986, Dr Engel has combined Japanese science and technology affairs with intellectual property research since 1987. Dr Engel received his PhD from Rockefeller University. LinkedIn: http://linkedin.com/in/alanengel, Contact: [email protected]
Published: 01st Sep 2010 in AWE International