Molecular and Histocytological Biomarkers - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 92

In situ exposure of the New Zealand mudsnail Potamopyrgus antipodarum along a gradi-
ent of Cd and Zn pollution induced histological lesions of the digestive gland, with hyper-
trophy of calcium cells and vacuolization of digestive cells (Gust et al. 2011). In Chinook
salmon ( Oncorhynchus tshawytscha ) and rainbow trout ( Oncorhynchus mykiss ), exposure to
copper (25 μg L -1 for 4 h) significantly reduced the number of olfactory receptors (Hansen
et al. 1999). In zebrafish embryos, a copper dose of 68 μg L -1 , responsible for histological
impairment (Johnson et al. 2007), is in the same order of magnitude of environmental
concentrations corresponding to low densities of fish populations in Michigan lakes (34.0
μg L -1 ) (Ellenberger et al. 1994). In both studies, histological damage parallels behavioral
disturbances.
4.3.3 Responses to Nanoparticles
As nanotechnologies are rapidly expanding, histocytological studies have been recently
reported in this particular field of ecotoxicology. Because many nanoparticles (NPs) are
electron-dense and electron probe microanalysis allows the determination of the elemen-
tal constituents of metallic particles, microscopic techniques are useful tools with which
to examine both the uptake and effects of NPs in organisms.
The liver of sticklebacks ( Gasterosteus aculeatus ) exposed to CdS NPs (5, 50, or 500 μg
Cd L -1 for 21 days) exhibited hepatocellular nuclear pleomorphism, with the most severe
cases recorded in individuals exposed to the highest dose; this liver pathology was not
observed in the control treatment (Sanders et al. 2008). Toxicity tests were performed to
investigate possible harmful effects on medaka ( Oryzias latipes ) exposed to nano-iron (0,
0.5, 5, 50 μg mL -1 ) for 14 days. No significant change was found in the liver and the brain,
whereas histopathological changes and morphological alterations were shown in the gill
and intestine (cell swelling, hyperplasia, and granulomas, etc.), which suggest that delete-
rious effects occur as a result of direct contact with nano-iron. Direct exposure through
the alimentary canal led to the accumulation of nano-iron in intestine tissues as confirmed
by microanalysis (Li et al. 2009). In the same species, exposure to Ag NPs (100-1000 μg L -1
for 70 days at early life stages of development) induced a variety of morphological malfor-
mations such as edema, spinal abnormalities, finfold abnormalities, heart malformations,
and eye defects in Japanese medaka ( Oryzias latipes ). Histopathological observations also
confirmed the occurrence of abnormal eye development induced by Ag NPs (Wu et al.
2010). Ultrastructural changes in the midgut of the microcrustacean Daphnia magna upon
exposure for 48 h to CuO NPs (at their 48 h EC 50 level = 4.0 mg CuO L -1 ) but not to bulk
CuO (also at 48 h EC 50 levels = 175 mg CuO L -1 ) indicate nanosize-related adverse effects
(Heinlaan et al. 2011).
4.3.4 Responses to Mixed Contamination
From the review by Au (2004) summarized in Table 4.3, one of the main limitations of the
use of histocytological biomarkers is their low specificity, with the exception of certain
disturbances linked to the presence of endocrine disrupting compounds in the medium
such as intersex (Chapters 8 and 9). In sites impacted predominantly by a particular class
of contaminants, as shown above for petroleum or metals, interpretation difficulties are
limited, but the situation is more bothersome in the case of complex mixtures. However,
histocytological biomarkers are highly appreciated for their sensitivity to chemical stress
in field studies.