Environmental Engineering Reference
In-Depth Information
Physiological Responses in Blood
Among the nine blood variables determined in the present work, only three
showed significant differences between the exposure groups; blood plasma chlo-
ride, blood glucose and blood partial pressure of CO
2
(pCO
2
) (Fig.
1
). The level
of plasma chloride in trout from the PI and the PI + SW tanks was significant
lower than in trout from the SW tank, indicating ion regulatory problems in
exposed fish. There is presently a broadly acceptance that the site of action of
acute toxicity of metals are in the gills
[19]
, and there are mainly two causes lead-
ing to a fall in plasma ions. Firstly, an increased passive efflux of ions across the
gills due to increased membrane permeability or disruption of the membrane, and
secondly an inhibition of active ion uptake by the chloride cells (e.g. reduced
Na/K-ATPase)
[20]
.
Metal exposure is mainly believed to affect the membrane permeability
rather than disrupting the chloride cells, although necrosis and apoptosis are
also observed in acute metal exposed fish
[21]
. Cu concentrations as low as
12.5 mg/L were found to lead to substantial loss of plasma ions in rainbow trout
(
Oncorhynchus mykiss.
)
[22]
, even in water at neutral pH and high Ca concen-
trations. In addition to a loss in plasma ions, an increase in the glucose levels
was observed. Such responses are also found in salmonids exposed to several
other elements, for example Pb
[23]
and Al
[16]
. A similar pattern was observed
in the present study, where both chloride and glucose showed a strong relation-
ship with several metals in the dissolved fractions, indicating multiple stress
responses (Fig.
2
). This is interesting; the high concentrations of DOC (5.84-
8.97 mg/L) and Ca (31.7-55.6 mg/L) measured in all the exposure tanks should
be sufficient to protect the trout against metal toxicity due to complexion pro-
cesses between dissolved metal ions and DOC, and due to Ca being a strong
competitor with high binding strength to biological membranes
[24, 25]
.
Particle bound Cu would likely be a source of Cu toxicity due to the lowered
pH in the gill mucus compared to surrounding water, thus favoring a transfer of
Cu ions from particles to the mucus matrix and finally into the gill tissue by
diffusion. Such processes could also be relevant for Cu complexed to organic
material
[26]
.
In the present study we also observed decreased levels of oxygen in the
waters, being lowest in the PI tank measured after 24 h (5.6 mg/L, ca. 50% satu-
ration at the actual temperature, Table
1
). There was a strong significant correla-
tion between dissolved oxygen in the water and the chloride concentrations in
trout blood (Fig.
2
). Blood acidosis is often related to severe hypoxic conditions,
with high pCO
2
(hypercapnia) in the water, and with specific changes with low-
ered blood pH and chloride, and increased TCO
2
and HCO
3
. However, there
were no significant differences between the exposure tanks regarding the latter
parameters (Fig.
1
), and they were not significantly correlated to the oxygen
concentration.
