Uptake of Organic Contaminants from Soil into Vegetables and Fruits - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 371

9.1 Introduction

A major concern of European citizens is residues of pesticides in fruits and veg-
etables (EFSA 2006 ). But not just pesticides pose a risk. In fact, for a whole range
of organic contaminants, uptake via diet is often the primary contribution to human
exposure (SCF 2002 ; Travis and Hattemer-Frey 1991 ). Contaminants may be taken
up into plants and subsequently accumulate in the human food chain (Czub and
McLachlan 2004 ) and affect the health of humans. Consequently, uptake of contam-
inants into plants is an essential part of most exposure models, for example CSOIL
(Brand et al. 2007 ), CLEA (DEFRA 2002 ) and EUSES (EC 2003 ).
About 20,000 plant species are used by the human race, and about 600 species
are cultivated (Franke 1987 ). Additionally, about 250,000 wild plants grow on earth
(Sitte et al. 1991 ). Thus, there is a large variability in plant properties. Also the
growth conditions vary, depending on soil type, soil properties, climatic conditions
and agricultural practice. Similarly, the number of organic contaminants is very
high. More than 5 million compounds have been synthesized. Around 30,000 com-
pounds are marketed in Europe, and contaminants released to the environment may
also be metabolized. Thus, from a researcher's point of view, the number of possible
combinations of plant species, contaminants and environmental conditions is close
to infinite. Nevertheless, general patterns are known and process-oriented models
have been established.
This chapter will give an overview of uptake processes of organic contaminants
from soil into plants, on prediction methods and on experimental results. Model
simulations will be carried out to identify the chemical properties that control the
accumulation in food crops. These predictions will be compared with experimental
results, in order to determine the potential of soil contaminants for accumulation
in food crops. For the calculation of exposure through vegetable consumption, see
Chapter 11 by Elert et al., of this topic.

9.2 Uptake and Transport Processes

Contaminants in the environment can enter plants by various ways (Fig. 9.1 ). The
main passive transport and uptake processes from soil are:

• uptake with transpiration water;

• diffusion from soil into roots;

• attachment of soil particles, eventually followed by diffusion into plant tissue.

However, contaminants can also be present in air. The main uptake processes
from air are:

• diffusive (gaseous) exchange with air;

• wet and dry particle deposition from air on plant surfaces followed by diffusion

into plant tissue.