Impairments of Endocrine Functions: Causes and Consequences - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 205

conclude that thyroid impairments could contribute to behavioral changes with ecological
consequences for estuarine fish and crustaceans (Table 10.2). Several studies with the fish
Pimephales promelas show an effect of EDCs on several parameters important for population
maintenance. Lange et al. (2011) have observed that a concentration as low as 0.2 ng EE2
L -1 was sufficient to induce a decrease in the number of eggs per female, concentration of
VTG in plasma, and the weight and size of larvae, whereas at 4.0 ng EE2 L -1 , the sex ratio
was female biased. In mature females exposed to 29-60 ng EE2 L -1 , both an increase and
a decrease in VTG concentrations were associated with a reduced reproductive capacity
(a reduction in the frequency of spawning that led to an overall reduction in the number
of eggs spawned) (Thorpe et al. 2007). Grist et al. (2003) have calculated that the intrinsic
growth rate of the population would be reduced to 0 if the environmental concentration of
EE2 was between 3.1 and 3.4 ng EE2 L -1 . Miller et al. (2007) have shown a highly significant
correlation between relative fecundity of P. promelas and VTG concentration in plasma. Yet,
several molecules, such as 17α-trembolone and 17β-trembolone, induce a consistent decrease
of VTG concentrations for experimental overloads of a few ng L -1 . These authors have mod-
eled changes of fish population size depending on the concentration of VTG in the plasma. A
reduction of VTG concentration by 50% would be responsible for population extinction after
20 years, a reduction by 75%, after 10 years. In killifish Fundulus heteroclitus from Newark
Bay, reduced egg production due to inhibition of vitellogenesis has been reported (Bugel
et al. 2011). However, the Newark Bay killifish population continues to sustain itself, as is
evidenced by young-of-the-year. A small percentage of the population appears to perform
the majority of the reproductive duties and may be why this population persists. In another
fish species, Poecilia reticulata , exposure to doses of 112 ng EE2 L -1 induced a dramatic change
in the sex ratio, which was highly female-biased, and significant reductions in male sperm
count with a subsequent drop in fertility in the exposed population (Kristensen et al. 2005).
Daouk et al. (2011) performed a life-cycle exposure using the zebrafish model and mixtures
representative of some environmental situations in terms of dietary doses and composi-
tion and containing mainly non-dioxin-like congeners. Under these realistic conditions, the
fertilization rate of fish spawns was decreased. Several mechanisms that could underlie the
reduction of fertility are reviewed, and additional examples of reduction are quoted.
In the fish Rutilus rutilus from wild populations living in effluent-contaminated rivers
in the United Kingdom, the intersex condition reduced reproductive performance by up
to 76% for the most feminized individuals, demonstrating a significant adverse effect of
intersex on reproductive performance. Feminization of male fish is likely to be an impor-
tant determinant of reproductive performance in rivers where there is a high prevalence of
moderately to severely feminized males (Harris et al. 2011), a situation frequently observed
in the field (Chapter 9).
The most convincing study showing a collapse of a fish population after exposure to
a synthetic estrogen has been carried out by Kidd et al. (2007). In a lake amended with
5-6 ng EE2 L -1 from summer 2001 to fall 2003, females of the fish Pimephales promelas had
higher VTG concentrations after exposure to EE2 when compared with reference samples
from another lake (reference lake fish had 2.5% of the VTG concentrations observed in
treated fish). More strikingly, in males, VTG concentrations were 3 orders of magnitude
greater than reference samples. Fish density was highly variable at the reference site, but
dramatically decreased in the presence of EE2. As a consequence, in the amended lake, no
recruitment occurred from 2002 to 2004.
Linking endocrine disruption and reproductive impairment with an ecologically rel-
evant impact has also been demonstrated in invertebrates (Chapter 9). In New Zealand,
the mudsnail Potamopyrgus antipodarum exposed in the field to WWTP effluents, cascading