PHYTOREM: In situ remendation of contaminated sites by hyperaccumulator plants

• Research unit: EU RFP
• Project number: 97.0362

Key words (English)

Phytoextraction; trace metals; salix; thlaspi; bioavailable; root system

Alternative project number (English)

EU project number: ENV4-CT97-0598

Research programs (English)

EU-programme: 4. Frame Research Programme - 3.1 Environment

Short description (English)

See abstract

Partners and International Organizations (English)

S.P. McGrath, IACR-Rothamsted (UK); J.-L. Morel, ENSAIA-INRA, (F); M. McLaughlin, CSIRO, (AU).

Abstract (English)

CET 'ABSTRACT' SERA PUBLIÉ PAR L'OFES. IL EST DONC IMPORTANT QUE LE FORMAT CI-DESSOUS SOIT CONSERVÉ.THE OVERALL OBJECTIVE OF THE PROGRAMME WAS TO PROVIDE KNOWLEDGE AND MATERIALS FOR FUTURE IMPROVED TECHNOLOGIES FOR PHYTOEXTRACTION OF METALS FROM SOILS. TO ACHIEVE THIS OBJECTIVE, THE FOLLOWING TYPES OF RESEARCH WERE CARRIED OUT. AT THE EPFL, WE FOCUSED ON 1) THE INVESTIGATION OF METHODS OF ENHANCING ACCUMULATION OF METALS BY NORMALLY NON-METAL ACCUMULATING HIGH BIOMASS CROPS, 2) THE IDENTIFICATION OF RHIZOSPHERE PROCESSES INVOLVED IN METAL REMOVAL BY HYPERACCUMULATORS AND HIGH BIOMASS CROPS. THIS WAS DONE BY MEASURING THE MOBILIZATION OF METALS IN THE RHIZOSPHERE AND THE CHANGES IN TOTAL AND BIOAVAILABLE AMOUNTS OF METALS IN TREATED SOILS AS WELL AS THE QUANTIFICATION OF THE POOLS OF METALS IN SOILS WHICH CAN BE REMOVED BY PHYTOEXTRACTION. ADDITIONALLY, THE PLANT AGRONOMY WAS STUDIED IN ORDER TO PROVIDE INFORMATION ON THE OPTIMAL WAYS OF MANAGING AND HARVESTING BOTH TYPES OF PLANTS FOR EFFICIENT METAL REMOVAL. THLASPI CAERULESCENS WAS TESTED AS CD AND ZN HYPERACCUMULATOR AND SALIX VIMINALIS AS HIGH BIOMASS PLANT IN TWO FIELD EXPERIMENTS. TOTAL OUTPUTS WERE HIGHER AT THE ACIDIC/ORGANIC SITE THAN AT THE CALCAREOUS ONE DUE TO MORE FAVOURABLE SOIL CONDITIONS (HIGHER BIOAVAILABLE POOLS OF METALS, LOW PH). IN THIS CASE PHYTOEXTRACTION SEEMED PROMISING AND COULD BE REACHED WITHIN A REASONABLE PERIOD OF TIME, AT LEAST FOR CD. ALSO, ACCELERATED ROTATION PERFORMED WITH THLASPI IN ORDER TO ENHANCE HEAVY METAL EXTRACTION DID NOT YIELD SUBSTANTIAL IMPROVEMENT. THE EFFECT OF THE ADDITIVES WAS RATHER POOR FOR BOTH PLANTS BUT A FE FERTILIZER HAD A POSITIVE EFFECT ON BOTH BIOMASS AND HEAVY METAL CONCENTRATIONS IN T. CAERULESCENS. HOWEVER THIS SPECIES GIVES HIGHLY VARIABLE RESULTS FROM YEAR TO YEAR WHEREAS TOTAL HEAVY METAL UPTAKE BY S. VIMINALIS SYSTEMATICALLY INCREASED WITH YEAR. OTHER PARAMETERS MAY BE RESPONSIBLE FOR THE DIFFERENT PLANT BEHAVIOUR AS FOR EXAMPLE THE SHOOT/ROOT RATIO (LARGER FOR THLASPI) AND THE EXTENT OF THE ROOT SYSTEM AND ITS FITTING TO THE SOIL CONTAMINATION. THE RELATIVE EXTRACTION EFFICIENCY OF THE PLANT DEPENDS ON THE SOIL AND CLIMATE CHARACTERACTERISTICS AND THE CHOICE WILL HAVE TO BE MADE ACCORDING TO THESE PARAMETERS AS WELL AS TO THE BIOMASS DISPOSAL FACILITIES. THE EFFECTS OBSERVED IN THE FIELD WERE CONFIRMED BY POT EXPERIMENTS. ADDITIONALLY, THE EFFECTIVE DECREASE IN TOTAL CD CONCENTRATIONS AFTER THLASPI GROWTH COULD BE QUANTIFIED. CADMIUM ASSOCIATED WITH ORGANIC MATTER WAS PREFERENTIALLY EXTRACTED IN THE ACIDIC SOIL WHEREAS CD BIOAVAILABLE IN THE CALCAREOUS BELONGED TO THE CARBONATE FRACTION. CARBONATE WAS HOWEVER A LIMITING FACTOR TO PLANT UPTAKE. USING PURE COMPOUNDS IN CONTROLLED CONDITIONS IT WAS POSSIBLE TO DETERMINE THE EFFECTIVE AFFINITY OF DIFFERENT SOIL COMPOUNDS (GOETHITE AND CRYPTOMELANE, CALCITE AND CHARCOAL) TO CD AND ZN AND THE EFFICIENCY OF THLASPI AND BRASSICA NAPUS (NON-ACCUMULATOR) IN EXTRACTING THOSE ELEMENTS FROM THESE COMPOUNDS. ISOTOPICAL TECHNIQUES (E- AND L-VALUE) SHOWED THAT CD AND ZN SORBED ON ORGANIC MATTER REMAINED FULLY BIOAVAILABLE WHEREAS FIXATION WAS MOST IMPORTANT ON CALCITE FOR CD AND ON CRYPTOMELANE FOR ZN. WHEN BIOAVAILABILITY WAS ASSESSED WITH PLANTS (THLASPI CAERULESCENS AND BRASSICA NAPUS), IT WAS FOUND THE LOWEST ON CALCITE FOR BOTH METALS AND THE HIGHEST ON CHARCOAL FOR ZN AND CHARCOAL AND ON GOETHITE FOR CD. THE RESULTS WERE PLANT DEPENDANT.FROM THE FIELD AND POT EXPERIMENT RESULTS IT APPEARS THAT DEPENDING ON SITE CHARACTERISTICS THE PLANTS MAY BE ABLE TO PERFORM PHYTOEXTRACTION WITHIN A REASONABLE TIME FOR SOME HEAVY METALS. IT WOULD BE HOWEVER NECESSARY TO PERSUE THE FIELD EXPERIMENTS ON LONGER PERIODS IN ORDER TO CONCLUDE DEFINITIVELY ON THE TIME NEEDED AS WELL AS THE FINAL CONCENTRATIONS (TOTAL AND BIOAVAILABLE) TO BE REACHED AND THE STABILITY OF THE SYSTEM.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 97.0362