Environmental Engineering Reference
In-Depth Information
can thus cause a rapid efflux of a wide variety of potentially toxic xenobiotics out
of the cells of aquatic organisms. This is a 'first line of defense' against endog-
enous and exogenous toxicants (Smital et al.
2004
; Kurelec
1992
; Epel
1998
).
However, some environmental chemicals act as specific MXR inhibitors and
have the potential to block the active efflux of xenobiotics, thereby causing a sig-
nificant increase of their intracellular accumulation. The main consequence of
inhibition is an increase in chemosensitivity of aquatic organisms toward the many
xenobiotics that are typically present in aquatic environments (Smital et al.
2004
).
Based on these considerations, otherwise innocuous environmental chemicals can
be seen as a new class of environmentally hazardous chemicals that are termed as
MXR inhibitors or chemosensitizers (Smital et al.
2004
).
Perchlorate is a very water-soluble and environmentally stable anion, which can
accumulate in plants (including lettuce, wheat, and alfalfa) and can thus contribute
to exposure in humans and animals (Richardson and Ternes
2011
).
8.2.1 Toxicological Impacts of Emerging Contaminants
Emerging contaminants and their transformation byproducts have adverse effects
on the health of aquatic organisms (including algae, bacteria and fish), of animals
and humans, as well as aquatic ecological effects (Guo et al.
2009
; Kumar and
Xagoraraki
2010
; Pal et al.
2010
; Derbalah et al.
2003
; Scully et al.
1988
; Jensen
and Helz
1998
; Jameel and Helz
1999
; Mitch et al.
2003
; Pomati et al.
2006
; Farré
et al.
2008
; Fairchild et al.
1999
; Boxall et al.
2004
; Jahan et al.
2008
; McLeese
et al.
1981
; Ahel et al.
1987
; Tyler et al.
1998
; Scott and Jones
2000
; Oberdorster
and Cheek
2001
; Cleuvers
2004
; Ferrari et al.
2004
; Bedner and MacCrehan
2006
;
Owen et al.
2007
). Their effects can be characterized using seven attributes: preva-
lence, frequency of detection, removal, bioaccumulation, ecotoxicity (for fish, daph-
nid, and algae aquatic indicator species), pregnancy effects, and health effects. The
latter attribute was characterized using seven sub-attributes: carcinogenicity, muta-
genicity, impairment of fertility, central nervous system action, endocrine effects,
immunotoxicity, and developmental effects (Kumar and Xagoraraki
2010
).
Production of byproducts such as trihalomethanes (THMs), N-nitrosodimeth-
ylamine (NDMA), and organic chloramines in conventional and advanced
wastewater treatment plants arises considerable concern. These compounds are
in fact extremely toxic and carcinogenic to human beings and aquatic organ-
isms, and have been found in drinking and natural waters (Scully et al.
1988
;
Jensen and Helz
1998
; Jameel and Helz
1999
; Mitch et al.
2003
; Farré et al.
2008
). Transformation products of some organics are often more persistent than
the corresponding parent compounds, and can cause greater toxicity (Boxall
et al.
2004
). For example, the major biodegradation product of nonylphenol ethox-
ylates, nonylphenol, is much more persistent than the parent compounds and has
estrogenic properties (Jahan et al.
2008
). Pharmaceuticals and their transformation
byproducts show acute toxicity to bacteria, algae, invertebrates, fish, mussels, and
human embryonic cells (Guo et al.
2009
; Kumar and Xagoraraki
2010
; Pal et al.
