Environmental Engineering Reference
In-Depth Information
Bowyer
1990
; Prasad et al.
1991
; Barraza and Carballeira
1999
; Susplugas et al.
2000
; Appenroth et al.
2001
; Franklin et al.
2001
; Drinovec et al.
2004
; Miller-
Morey and van Dolah
2004
; Shanker et al.
2005
; Alam et al.
2007
; Hayat et al.
2007
; Perales-Vela et al.
2007
; Ali et al.
2008
; Hasan et al.
2008
; Vernay et al.
2008
). The esterase activity in several species of marine and freshwater cyano-
bacteria can be either enhanced or suppressed by copper (Franklin et al.
2001
),
and antimony (Sb) exposure at concentrations ranging from 1.0 to 10.0 mg L
−
1
inhibits O
2
evolution (Zhang et al.
2010
). A decrease in photosynthetic efficiency
is caused by the reduction of phytoplankton enzyme activity, which may be a gen-
eral indicator of cell stress. The stimulating action of Cu for a definite concentra-
tion level (e.g. 0.02 mg Cu L
−
1
) on PSII system is often observed in natural waters
(Franklin et al.
2001
; Burda et al.
2002
; Schaffer and Sebetich
2004
).
Toxicity of Cd and Zn to the green alga
Pseudokirchneriella subcapitatais
can be significantly (p < 0.05) reduced in the presence of humic acids (soil and
peat), but not in the presence of Suwannee River fulvic acid (SRFA) (Koukal et al.
2003
). It is postulated that humic acid can reduce Cd and Zn toxicity in two differ-
ent ways (Koukal et al.
2003
): (i) Humic acid is capable of decreasing the amount
of free metal ions through complex formation with the metal. Humic acid has high
molecular weight and is relatively stable with regard to metal-exchange reactions,
which can make the metals less bioavailable. (ii) Humic acid can be adsorbed onto
algal surfaces, shielded the cells from free Cd and Zn ions. On the other hand,
several hypotheses have been advanced to explain why SRFA is unable to reduce
metal toxicity (Koukal et al.
2003
): (i) Cd- and Zn-SRFA complexes are thought
to be labile (i.e. to undergo rapid dissociation); (ii) SRFA can coagulate, presum-
ably during equilibration, which can alter their metal complexing behavior; and
(iii) SRFA has a low ability to adsorb on cell membranes at pH > 7.
For better understanding the mechanism of metal toxicity to organisms, it
is interesting to have a look at the outer-shell electronic configurations of toxic
metals:
As
33
: 1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
3
d
10
4
s
2
4
p
3
and As
3
+
: 1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
3
d
10
4
s
2
4
p
0
;
Sb
51
: 1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
3
d
10
4
s
2
4
p
6
4
d
10
5
s
2
5
p
3
and Sb
3
+
:1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
3
d
10
4
s
2
4
p
6
4
d
10
5
s
2
5
p
0
;
Zn
30
: 1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
3
d
10
4
s
2
and Zn
2
+
: 1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
3
d
10
4
s
0
;
Cd
48
:
1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
3
d
10
4
s
2
4
p
6
4
d
10
5
s
2
and
Cd
2
+
: 1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
3
d
10
4
s
2
4
p
6
4
d
10
5
s
0
;
Cr
24
:
1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
4
s
1
3
d
5
and Cr
4
+
: 1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
4
s
1
3
d
1
Cu
29
:
1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
4
s
1
3
d
10
and Cu
2
+
: 1
s
2
2
s
2
2
p
6
3
s
2
3
p
6
4
s
1
3
d
8
These metal ions have empty
s
-,
p
- or
d
-orbitals in the outer shell, which allows
them to be involved in a strong
π
-electron bonding system through donation of
electrons from the functional groups of PSII (e.g. N- and S-containing carbox-
ylic, amino, thio and hydroxyl groups) (see chapter
“
Complexation of Dissolved
Organic Matter With Trace Metal Ions in Natural Waters
”
for detailed discussion)
