I specialise in the behaviour of trace contaminants within the biosphere, including radionuclides, trace elements, organics and biological substances.
A wide variety of environmental contaminants originates from man's industrial, military and agricultural activities. Most contaminants are present in the environment at low concentrations, although considerable uncertainty surrounds our understanding of the impacts many of these have on humans and the environment in general. Recent examples include a diverse range of radionuclides from nuclear facilities, depleted uranium from military activities, organophosphate pesticides from sheep dip and prion proteins from TSE infected sheep and cattle. Throughout my research career I have used a combination of laboratory and field-based experiments, environmental measurements and computer modelling to quantify and understand processes of contaminant migration, persistence and sequestration. The overall aim of my research is to improve our ability to evaluate the risks posed by contamination of the environment and to assist in the design of remedial solutions.
My research career began in 1987 and has focussed on the problem of radionuclide transmission from contaminated soils into plants and thence into the food-chain. After carrying out postdoctoral research for the Central Electricity Generating Board I joined an interdepartmental research group within Imperial College which carried out an integrated programme of research into sub-surface to surface migration of radionuclides in soils as part of the UK Nirex Biosphere Research Programme. From 1988 to 2005, experiments involved field lysimeter, soil column and laboratory studies and shared information with nuclear waste disposal agencies in Canada, Japan, France, Sweden and others. Results from lysimeter studies were internationally reviewed and some of the data obtained were used in model validation studies conducted by the International Atomic Energy Agency (BIOMOVS II and BIOMASS programmes).
In recent years a key interest has been in the migration and plant uptake of radioactive chlorine, iodine, technetium, caesium, strontium and selenium under both static and dynamic hydrological conditions. With EU funding, these measurements have been accompanied by the development of comprehensive databases of stable element concentrations, moisture contents and oxidation-reduction potentials which are currently being used to develop an improved understanding of solid-liquid partitioning within variably saturated soils.
A key finding of lysimeter and related research into radioactive chlorine migration was the formation of humic-chlorine associations which has implications for the potential behaviour of chlorine-36 migrating from nuclear waste repositories into future boreal ecosystems with highly organic soils. This also has major implications for the biogeochemical cycling of non-radioactive chlorine.
During the 1990s I was involved in research into the interaction of airborne particulates, gases (carbon-14) and vapours (tritiated water) with plant canopies. These studies were based primarily in wind tunnel and rain simulator facilities and, amongst other things, involved development of a technique to generate monodisperse aerosols from depleted uranium solutions which were subsequently used to obtain sensitive measurements of particle deposition to tree tissues.
In the aftermath of the Chernobyl accident I was involved with the European Commission's radiation protection research programme and joined a joint EU-former Soviet study group evaluating the long-term fate of radionuclides contaminating forest ecosystems within the Chernobyl 30km exclusion zone. My specific interests in this study were to gather field data on the contrasting behaviour of radionuclides in forests in the near- and far-field (Ukraine, Belarus and western Europe, respectively) and to provide predictions of the long-term consequences of this contamination. This work developed into numerous collaborations with research groups within the former Soviet Union and the European Union. It also led to my involvement with several exercises conducted by the International Atomic Energy Agency for which I have acted as consultant on the problem of radioactive contamination of the forestry industry within Belarus as well as helping to devise a methodology to assess radiation doses to the public from radionuclides in timber and wood products. During the IAEA's BIOMASS programme (1998 - 2001) I chaired the Forest Working Group which carried out a review of international forest modelling expertise and a series of model inter-comparisons with participants from research groups from Europe, Japan and the USA.
Over the last decade my interest in trace radioactive substances has led to studies on other trace contaminants, including potentially toxic or oestrogenic organic compounds in soils. I have been involved with research into the sorption and longevity of several such compounds in soils including herbicides (2,4-D, isoproturon and trifluralin), veterinary medicines (synthetic pyrethroids and organophosphates) and oestrogen mimics (alkyl phenols).
I recently contributed to a European Commission funded study on the risks posed by the disposal of animal carcasses infected with transmissible spongiform encephalopathies such as BSE or scrapie. A major focus of this work was the development of suitable techniques to extract the prion protein (PrP) from soil matrices, and the quantification of sorption and migration of PrP in soil columns under controlled hydrological conditions.