Agriculture Reference
In-Depth Information
Within the existing agriculture model, agrochemicals are classified as one of the main
chemical pollutants that are disseminated throughout the planet (Grisolia, 2005). However,
there is still little information about the effects of these chemical compounds on
invertebrates that occupy levels of high sensitivity in trophic chain (Mantecca et al., 2006).
Among the studies carried out with terrestrial invertebrates it was analyzed the possible
alterations in the biomass (Niemeyer et al., 2006a), reproduction (Helling et al., 2000),
behaviour (Niemeyer et al., 2006b), survival (Diao et al., 2007) and tissular and cellular
lesions (Nasiruddin & Mordue, 1993) resulted from exposure to certain agrochemicals.
Associated with the use of bioindicators and biomarkers it is also used the direct analysis of
the presence of residues in soil samples by specific equipments such as the
spectrophotometer or chromatograph.
Pesticides have been widely tested by bioassays with plants and positive results are usually
obtained (Leme & Marin-Morales, 2009). A clear example is the
A. cepa
test successfully used
in the evaluation of the mutagenic and genotoxic potential of herbicides such as trifluralin
(Fernandes et al., 2007; 2009).
2.6 Metals
Heavy metals or trace metals are terms applied for a great amount of trace elements that are
industrially and biologically important. From the point of view of human health, agriculture
and ecotoxicology, the most worrying heavy metals are As, Cd, Hg, Pb, Ti and U. Studies
involving heavy metals in ecosystems have shown that many areas near urban centres,
mines and road systems have high concentrations of these elements (Alloway, 1994). Metals
are highly persistent in the soil with persistence of up to thousands of years (McGrath, 1987)
and can express their pollutant potential directly on the soil organisms by availability to
plants and transference to the food chain, both by plants and by the contamination of
superficial waters or groundwater (Chang et al., 1987).
The main anthropogenic sources of metals are fertilizers, pesticides, contaminated irrigation
water, combustion of coal and oil, vehicular emissions, incineration of urban and industrial
wastes and, mainly, mining and smelting (Tavares & Carvalho, 1992).
Due to their habits in the superficial layers of the soil, invertebrates of the saprophagous
fauna, such as isopods, diplopods and springtails are regularly exposed to metals (Hopkin,
2002). Heikens et al. (2001) carried out a literature review to clarify the concentration of
metals in terrestrial invertebrates and they concluded that the concentration in most of the
groups happened in the order Pb>Cd>Cu. Afterwards, Köhler (2002) conducted a study to
determine the location of these metals in the bodies of soil arthropods. The genotoxic
potential of metals has also been studied by several authors using plants as test systems
(Knasmüller et al., 1998; Rank & Nielsen, 1998).
3. Invertebrates of the edaphic fauna and higher plants as soil bioindicators
One important question in ecotoxicological studies refers to the choice of the bioindicator
species. It will depend on its ecological and toxicological importance, facility to be
maintained in laboratory, reproductive rate and sensitivity (it must be affected by several
chemical agents but less affected by abiotic factors) (Römbke & Garcia, 2000). Many authors
agree that the main features needed to be a good bioindicator are sensitivity, good
representativeness and functional importance in the ecosystem, as well as easy collection,
identification and analysis (Greensdale, 2007). In this context, some taxonomic groups of soil
invertebrates and higher plants have been proposed as bioindicator organisms.
