Environmental Engineering Reference
In-Depth Information
Iron precipitates may also be taken up by aquatic organisms in their food
and the presence of iron-enriched food can actually reduce the absorption
of Fe via the gut membrane by causing the formation of Fe hydroxide
precipitates on the gut wall (Gerhardt
1995
).
As well as affecting individual macroinvertebrates, iron and aluminium
contamination and the resulting suspended solids were also found to be an
important factor in affecting community structure (Gower et al.
1994
; Auladell
2009
). McKnight and Feder (
1984
) and Sasaki et al. (
2005
) reported that macro-
invertebrates were inhibited when the riverbed was covered with metal pre-
cipitates. Grazers feeding on periphyton and other biofilms have been reported
to be the first invertebrates eliminated by increasing Fe concentrations
(Rasmussen & Lindegaard
1988
). Increased drift of invertebrates has also been
reported to be caused by an increase in suspended solids (Gammon
1970
; Ryder
1989
), and this has also been linked to changes in drift in response to acid mine
drainage (Elliott et al.
1988
).
The proliferation of certain groups in communities impacted by iron-rich
discharges could reflect the adaptation of certain taxa to living in deposited
sediments such as oligochaetes and some chironomids (Wiederholm
1984
;
Mackay
1992
; Smith
2003
). This correlates with the changes in communities
reported downstream of mine drainage (see earlier).
Iron hydroxides are also extremely reactive substances and other metals can be
sorbed to their surface (e.g., He et al.
1997
), posing a toxicological risk to inverte-
brates within the system in terms of direct uptake through food (see section below).
This suggests that, where metalliferous discharges are dominated by iron (or
aluminium and to a lesser extent manganese), the processes by which organ-
isms are impacted are very different from those for non-ferruginous waters.
This has implications not only in the assessment of impacts using biological
indices (the differential response by groups of organisms and individual species
suggests that a simple biological index such as BMWP would not be sufficient)
but also on the recovery following remediation activities.
Uptake and bioaccumulation of metals
The presence of adapted organisms within metal-contaminated environments
may pose a risk to the food chain. This will depend upon whether metals are
taken up within the receiving organisms and are bioaccumulated or biomag-
nified up the food chain. Within aquatic environments, organisms can take up
metals directly through the water column (Rhea et al.
2006
) but they may also
be taken up via food or when burrowing in sediments.
The majority of studies have shown that macroinvertebrates are able to take
up metals from sediments with direct relationships between tissue and sedi-
ment concentrations of Cu, Cd, Zn and Pb being demonstrated for chironomids
