Biogeochemistry of trace elements

Chapter 1. Trace elements in the environment: retrospect and prospect

Printed on Sep. 13, 2004

Zueng-Sang Chen ()

Introduction

Micronutrient and toxic elements in 1937

Trace elements in soils and plants

Historical retrospect

Nine trace elements for plants: B, Cl, Cu, Fe, Mn, Mo, Ni, Na, and Zn

14 trace elements for animal: Si, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, I, and F)

Trace elements: Bd> 6g/cm3

Rachel Carson’s book Silent spring: pollution of phosphate and nitrate

Minamata (methylmercury poison) and Itai-itai (cadmium) diseases in Japan

New analytical techniques and equipments: relatively easily , rapid, and reliable analysis

Orchard insecticide spray (leas arsenate), lead in roadside, pollution by Cu and B, Zn-induced chlorosis

Color of deficiencies symptom published by Wallace T. (1943)

Low bioavailability of Pb and soil factors

Prospect

Sampling and analysis

Water and blood sampling are arguably the most advanced

Stream sediments sampling method

Soil sampling method is lack

Local variability (CV%)

Research is need for soil heterogeneity

Baseline, Background, Average, and Contamination

Pedological approach: soil series, pedon, major group soils, soil Order

Hypothesize: it can be described in terms of mean and range of values of trace elements

Distribution of trace elements in soils is log-normal, not normal

Is complex and irregular in geological materials

Baseline: unaffected by human activity

Background: general conc. Of trace elements found in a particular area

Contamination: conc. Is enough to cause harm to some organism

Case studies of geometric mean of Pb in England and Wales in last Para. in page 9

Mathematic mean, geometric mean, median

Chemical forms, speciation, and Bioavailability of elements

Soluble fractions have a biological significance

Soil chemists approach to establish the soil extractants

Two major and popular reagents are EDTA and DTPA

Which extractants can predict the metals uptake?

Models to explain the soil contents vs. uptake.

Baker, A.J.M. (1981): Accumulators, indicators, and excluders.

Campbell et al. (1989) reviewed the techniques for obtaining soil solution from field-moist soils

Saturation extract, pressure extracts, fixed ratio water extracts for routine tests of soils

Nutrient uptake by roots releasing solubilizing agents

Sposito G. (1983): GEOCHEM to predict the chemical species in aqueous solution given certain conditions

McLaren and Crawford (1973): Five fractionation of Cu in soils: soil solution and exchangeable, weakly bounded, organically, oxided bounded, and residual form.

Modeling

Published works should lead to hypotheses which can be tested

Predicted models can be derived

Models of elements in soils-plants-food chain systems is need to be established

Trace elements and Health

Human cancer might be linked to biogeochemical environments

Toxicological problems of Pb and Cd are dominated in last 25 years

Pb in blood affect on the enzyme activity

Cd and Hg are another stories

Extra reading:

Tinker PB. J. Soil Science 37: 587 (1986)

Jackson KW et al., Soil Science 143: 436 (1987)

Soon YK and TE Bates. J. Soil Science 33: 477 (1982)

Baker AJM. J. Plant Nutrition 3: 643 (1981)

Campbell DJ et al., J. Soil Science 40: 321 (1989)

Sposito G. The chemical forms of trace elements in soils. London Academic Press 1983.

McLaren RG and D Crawford. J soil Science 24: 172 (1973)

Discussion:

Representative sample

Sampling methods

Bioavailable concentration by soil testing, soil solution, etc.

Uptake model of crops

Baseline or background concentration

Speciation by models, by analysis

Fractionation methods

Risk assessment

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Biogeochemistry of Trace elements: Chap.1