Agriculture Reference
In-Depth Information
effect measured in acute toxicity studies with aquatic organisms is lethality or some
other body event that precedes it, for example, the state of immobility (Costa
et al.
2008
).
Chronic toxicity tests, in turn, are conducted to measure the effects of chemicals
on water for a period that may cover part or all of the test organism species life
cycle. The fact that a chemical does not produce toxins for aquatic organisms in
acute toxicity test effects does not indicate that it is not toxic to them. Chronic
toxicity tests allow us to evaluate the possible toxic effects of chemicals under
conditions of prolonged sublethal concentration exposure, i.e., concentrations that
permit the survival of organisms, but that affect their biological functions, such as
reproduction, egg development, growth, and maturation, among others (Kendall
et al.
2001
; Ronco et al.
2004
).
Toxicity tests can be further classified into static, semi-static, and dynamic,
according to the method of addition of the chemicals solutions. The static tests
are performed without the renewal of the test solutions and are recommended for
samples that do not cause oxygen depletion, which are not volatile and are stable in
aqueous medium. On the other hand, unstable or volatile toxic substances have their
concentrations reduced throughout the test, contributing to the underestimation of
the result. In such cases, the semi-static tests, in which the solutions are renewed
periodically, are recommended. The long-term chronic toxicity tests are usually
performed in dynamic mode. In dynamic testing, the test solutions are continuously
renewed (APHA
1998
; Adams and Rowland
2003
; ABNT
2004
).
13.4 Characterization of Materials for Ecotoxicology Is
Essential
The acquired experience in ecotoxicology throughout the years allows the affirma-
tion that not only the size influences the reactivity of nanomaterials but also a wide
range of other properties that must be evaluated when conducting toxicological
tests, and physico-chemistry is paramount when trying to understand the fate and
behavior of the particles in the environment (Brayner et al.
2010
). For Jiang
et al. (
2008
), for example, until the relationship between the characteristics of
nanoparticles and toxicity is fully understood, it will be necessary to ensure that
all potentially significant characteristics are measured.
Since the determination of all these features is virtually impossible, some
authors have identified a number of key properties that must be addressed in
toxicology studies, which are size, dispersion state, surface charge, shape, chemical
composition, surface area, and surface chemistry (Oberd¨rster et al.
2005a
,
b
;
Powers et al.
2006
). These factors play important roles in the uptake and distribu-
tion of the particles within live organisms (Brayner et al.
2010
). If not determined,
the possible toxic effects could not be easily attributed to a certain property of the
