Agriculture Reference
In-Depth Information
(Spain 1998) or Baia Mare/Borsa (Romania 2000). During the course of these accidents, huge
amounts of mine waste and toxic substances (heavy metals, cyanide) were set free in one go,
contaminating rivers and alluvial soils (Kemper & Sommer 2002). Pyrite oxidation is one of
the most acid-producing natural weathering processes, in which trace metals are mobilized
and released into the river system and groundwater. It is a complex process that proceeds
rapidly when pyrite is exposed to air. In a first step, pyrite produces a solution of ferrous
sulfate and sulfuric acid. The dissolved ferrous iron continues to oxidize and hydrolyze,
producing additional acidity. During the oxidation process, the pyrite transforms first to
copiapite, then to jarosite, schwertmannite, ferryhydrite and eventually to hematite or
goethite (Kemper & Sommer 2003).
Based on the sulfur content, other information can also be derived. Sulfur plays a key role in
the assessment, because it is one of the two elements forming pyrite (FeS
2
), which is the
main component of the sludge (75-80% wt), and it is the main source of acidity when pyrite
oxidizes. The sulfur content is also used in conventional mining waste analysis for the
prediction of its geochemical behavior and to identify wastes that are likely to be acid-
generating or susceptible to heavy metal leaching (Kemper & Sommer 2003).
6. Pesticides
Soil contamination by agricultural pesticides is a matter of increasing concern. Several
authors have reported accurate predictions of pesticide sorption to soil using NIRS.
Bengtsson et al. (2007) used NIRS to predict lindane and linuron sorption to soil samples.
The pesticide-content predictions were established by PLS of the VNIR-SWIR spectra and
sorption data obtained using the batch equilibrium technique. PLS could predict 85% of the
soil sorption (Kd) for lindane and 84% for linuron, respectively. Later, Brunet et al. (2009)
tested the feasibility of determining chlordecone contamination in soils. Chlordecone, also
known as kepone, is a chlorinated polycyclic ketone pesticide. It is toxic, persistent, and
induces cumulative and delayed toxicity. The regular method to measure chlordecone
involves extraction with two solvents and quantification by gas chromatography-mass
spectroscopy. A total of 236 samples were collected at 0-30 and 30-60 cm depths in
Andosols, Nitisols and Ferralsols from all over the eastern part of Martinique (French West
Indies). Chlordecone content was determined by wet chemistry and the reflectance spectra
were recorded. Modified PLS (mPLS) regression was used to correlate spectral data to
conventional values. While conventional measures and NIRS predictions correlated poorly
at high chlordecone contents (>12 mg kg
-1
), when the validation set was divided into four
classes based on chlordecone content, NIRS prediction properly classified 80% of the
samples (Brunet et al. 2009).
7. Vegetation stress as an indicator for soil contamination
The concept of using plants as indicators for soil contamination has been tested for many
years, for many good reasons: 1) inorganics in general do not exhibit characteristic
absorption features in the VNIR-SWIR wavelength region; 2) the plant's root system is
susceptible to contaminated material, and extracts and transports it to the aboveground
plant parts, and 3) soil is far from always being bare; it is often covered with plants. Free
metal ions in the soil solution and exchangeable ions of clays and OM are mostly available
for plant uptake (Lasat 2000). For their development, plants require not only macronutrients
