*A report of the International
Conference on the Biogeochemistry of Trace Elements, held at the Technical University,
Vienna, Austria during 1115 July 1999.
regulation of plant-based processes involved in the
entry of toxic heavy metals into the food chain (via uptake into plants), the
phytoremediation of metal contaminated soil and mechanisms of heavy metal tolerance by
plant. Referring to the soil as a primary source of essential trace elements for plants,
animals and therefore, for humans, Thornton pointed out that soil is also a source of
heavy metals, though anthropogenic inputs of industrial and other emissions may greatly
exceed natural geological sources.
The conference topics covered important aspects of
fundamental research such as kinetics and mechanisms of the fate of trace elements,
radionuclides, in the soil and related ecosystems and methods of their assessment. The
scientific programme comprised ten special symposia, emphasizing key areas in trace
element research.There were 298 oral presentations in 59 special symposia and technical
sessions as also three poster sessions consisting of nearly 253 papers.
Alan Baker (UK) described that specially selected
plants, e.g. Thlaspi species, known as hyperaccumulators, can extract and
accumulate exceptionally high levels of toxic metals from the soil. Phytoremediation is a
new technology employed for removing excessive toxic metals and pollutants from the soil
or contaminated aqueous medium. Louis Jean Morel (INRA, France) explained that human
activities lead to the ineluctable increase of metal concentrations in the soil and are
becoming a threat for the surrounding ecosystems and for food safety. Hyperaccumulators
are a special class of plants which have acquired the ability to accumulate metals with
higher than 1% concentration in the foliar dry matter. Steve P. McGrath (Rathamsted, UK)
explained constraints to the growth and metal uptake by hyperaccumulator plants. Rufus L.
Chaney (USDA-ARS-Environmental Chemistry Lab, USA) concluded that development of effective
agronomic management practices and improved cultivars of hyperaccumulator species show
promise for development of successful phytomining and phytoremediation technologies for
Ni. Clayton L. Rugh and co-workers (University of Georgia, USA) demonstrated that transfer
to bacterial mercury resistance genes to plants provide them the ability to grow on
normally toxic Hg-containing substrates and has great potential as a method to remove
hazardous bioavailable mercurials from contaminated environments.
S. Dushenkov (Ukraine) concluded that
phytoremediation may be a valuable option for the soil with low level radionuclide
contamination. High biomass plants are capable of removing substantial amount of
radioactivity from the soil. T. Harren (Switzerland) opined that to achieve better results
either in modelling of radionuclide soil-to-plant transfer or in phytoextraction further
research in the soil chemical processes and in the plant uptake mechanism is needed.
Hirofumi and Tsukada (Japan) suggested that the investigation of the root uptake of stable
Cs and K in the rice plant could lead to a better understanding of the transfer of
radiocesium in paddy fields. E. Lombi (UK), W. W. Wenzel (Austria), G. R. Gobran (Sweden)
and D. C. Andriano (USA) reviewed the work on rhizosphere-contamination interaction and
its role in phytoremediation and suggested that future research should be directed to
establish the role of rhizosphere processes in the various phytoremediation technologies
on a metal-specific basis.
N. T. Basta (Oklahoma State University, USA) and G.
M. Pierzynski (Kansas State University) discussed the remediation technologies of As, Pb,
Cd and Zn contaminated soils and explained that smelting of non-ferrous metal ores,
pesticides, coal combustion, and Pb-based paint atmospheric deposition have resulted in
contamination of the urban soil with these heavy metals. Chronic exposure to these
contaminants can result in human health effects including kidney dysfunction from Cd, skin
and internal organ cancers from As and impaired metal development from Pb. Excessive Zn
and Cd in the soil causes phytotoxicity. B. D. Hill and R. Naidu (South Australia)
provided a brief overview of issues of soil contamination within Australia, New Zealand
and the South Pacific region and current assessment, management and remediation strategies
that have been developed for addressing these issues. They reported that there are
approximately 60,000 contaminated sites in Australia and over 50,000 in New Zealand and
the South Pacific region. M. H. Wong (China) presented current approaches to managing and
remediating metal-contaminated soil in China and M. G. Pirzynski in the United States.
Similarly, K. M. Paknikar (India) discussed bioremediation of metal contaminated soil
strategies for India and its neighbouring countries. Chakraborti (Jadavpur University,
India) cautioned that the arsenic calamity of West Bengal, which is one of the biggest in
the world, should not be neglected and similar situations should be avoided in other
countries. A proper watershed management is the need of the day. S. M. Ullah (Dhaka
University, Bangladesh) predicted that the entry of metals into the food chain through
plant uptake might cause health hazards and also environmental problems. Mobilization of
metals due to their complexation may play an important role in the soil after
aforestation, in particular after agricultural application of organic fertilizers as
concluded by A. Karczewska (Poland). G. Taylor (Canada) suggested that a more detailed
analysis of the potential for interactions between metals in the environment may be
required. Marigold is able to take chromium in quite large quantities as suggested by C.
Bini (Italy) and could be suitable for phytoremediation of Cr-affected soil. Over 30
metallic elements and 20 nonmetallic elements have been found in crude oils by S. L.
Davydova from Russia who further predicted that heavy metals will be the main pollutants
of the next century. Naidu revealed that electrokinetic remediation and soil washing
process may be useful technologies for the removal of As from contaminated soils. Studies
conducted by C. Michiel Laker (South Africa) suggest that Mn deficiency may increase the
incidence of oesophogeal cancer and it is important to understand the interrelationship
between the soil, crops and human health.