Environmental Engineering Reference
In-Depth Information
and are environmentally unrealistic (see Buikema & Voshell
1993
for a compre-
hensive review). However, many of, and in fact the majority of, metalliferous
discharges within the environment have a number of different metals within
them, and in fact can contain other contaminants such as Polyaromatic Hydro-
carbons (PAHs) (e.g., Tiefenthaler et al.
2008
). This can have a significant effect
upon the bioavailability and toxicity of the elements to organisms. There are
three basic ways in which they can interact with each other (Gerhardt
1993
):
1. Additivity. This occurs where the action of the combined pollutants is
equal to the sum of the individual effects.
2. Synergism. The action of the combined pollutants is greater than the sum
of the individual effects.
3. Antagonism. The action of the combined pollutants is less than the sum of
the individual effects.
There have been limited investigations into the interactions between two
or more metals and their effects on biota within the same environment.
An antagonistic effect was found to occur between Zn and Cd in Daphnia magna
(Bat et al.
1998
; Barata et al.
2002
; Komjarova & Blust
2008
). Both additivity and
antagonism have been reported in previous studies of AMD toxicity in fish
(Finlayson & Verrue
1982
). Studies in a mining catchment in West Virginia
showed that the impacts on biota were a result of a suite of chemical constitu-
ents (Al, Ni and Mn) rather than a single critical toxin (Freund & Petty
2007
).
The individual concentrations of toxins were at levels lower than the critical
threshold value for biological impairment, and the toxic effects were possibly
due to the interactions between multiple stressors. Amphipods were also
reported to show greater responses to a mixture of metals, rather than a single
contaminant (Besser et al.
2009
), and toxicity has also been found to increase in
Daphnia magna (Negiliski et al.
1981
; Biesinger et al.
1986
). However, suppression
of metal uptake has also been reported to occur in amphipods with uptake of
Cu, Ni and Zn being suppressed by Cu (Komjarova & Blust
2008
). The reported
metal interactions were found to predominantly occur at low concentrations
where binding sites are not completely occupied. Interactions in field condi-
tions are, therefore, likely to be dependent upon the concentrations of metals
within the water column together with the mixture of metal species. The
potential importance of the interaction between organic and inorganic pollu-
tants has not been adequately researched to date.
The diversity and abundance of macroinvertebrates has been found to be
reduced in the presence of metals such as Cu and Zn, independent of pH
(Soucek et al.
2000
; Hickey & Golding
2002
; Hirst et al.
2002
). More specifically,
mayflies have been reported to be significantly affected by the presence of
metals (Cu, Zn, As) with a loss in numbers (Mori et al.
1999
; Hickey & Golding
2002
). This agrees with overall responses to metalliferous discharges. However,
