Uptake of Metals from Soil into Vegetables - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 326

Contents

8.1 Introduction ............................................ 326

8.2 Metal and Metalloid Chemistry in Soil ........................... 326

8.2.1 Cationic Metals ......................................

327

8.2.2 Anionic Metals/Metalloids ...............................

329

8.2.3 Effects of Soil Redox .................................. 330

8.3 Plant Acquisition of Metals and Metalloids from Soil .................. 331

8.3.1 Root Uptake Pathway .................................. 331

8.3.2 Foliar Uptake of Metals .................................

344

8.4 Integrating Factors Affecting Metal/Metalloid Accumulation by Vegetables ..... 348

8.4.1 Type of Metal/Metalloid ................................

348

8.4.2 Vegetable Species .................................... 349

8.4.3 Vegetable Cultivar .................................... 350

8.4.4 Soil Physical/Chemical Properties .......................... 350

8.5 Models to Predict Contaminant Uptake by, or Toxicity to, Vegetables ......... 354

8.5.1 Model Characteristics ..................................

355

8.5.2 Application of Models ................................. 359

References ................................................

360

8.1 Introduction

The transfer of metal (and metalloid) contaminants from soil, through plants, to
humans, may be an important exposure pathway in some urban and residential envi-
ronments. This exposure pathway may also be important for agricultural land-use
scenarios to manage exposure of the general population to metals and metalloids.
This chapter summarises our current understanding of metal/metalloid behaviour in
soils, uptake and transport of these elements by plants, and the current models and
concepts used to predict exposure of humans to metals and metalloids through a
food-chain pathway.

8.2 Metal and Metalloid Chemistry in Soil

In describing the chemistry of metals and metalloids in soil, distinctions need to
be drawn between the behaviour of cationic and anionic elements given the impor-
tance of surface charge to the fate and behaviour of elements in soils (Sposito 1981 ,
1989 ). Most topsoils have a net negative surface charge, with exceptions being soils
rich in iron, aluminium or manganese oxides and depleted in organic matter and
phosphorus (P) or sulphur (S). These latter soils, which may have a significant net
positive charge, are found in tropical regions, particularly in subsoils (Wong and
Wittwer 2009 ). Soils with net negative charge retain cationic metals more strongly,
soils with net positive charge will retain anionic metals more strongly. Hence we
will discuss the behaviour of cationic and anionic metals separately. A further key