Page 868 - The Toxicology of Fishes

848 The Toxicology of Fishes

1972); thus, the concentration of DDT in salmonine eggs required to cause lethality was determined to
be between approximately 1.0 and 10 mg/kg egg ww. The concentrations of DDT in salmonine eggs
from the Great Lakes are currently in the range of 0.1 to 1 mg/kg egg ww (Hickey et al., 2006), depending
on species and location. In 1984, the concentrations of DDT in Chinook salmon eggs from Lake Michigan
were 1.2 mg/kg ww (Giesy et al., 1986). Historically, concentrations of DDT were as great as 20 mg/kg
ww in eggs of fishes from the Great Lakes (Atchison, 1976; Burdick et al., 1964; Hopkins et al., 1969;
Johnson and Pecor, 1969). When the correlation between rearing mortality was considered, some
investigators found a correlation but others did not; for example, concentrations of DDT between 2.0
and 9.4 mg/kg egg ww in Coho salmon were not correlated with rearing mortality (Mason et al., 1967).
In a similar study of the relationship between rearing mortality of Lake Michigan Chinook eggs and fry,
no relationship was found between concentrations of the DDT complex and any of the hatching or
survival of eggs or fry (Giesy et al., 1986); thus, the concentrations of DDT observed historically in
Great Lakes salmonines were in the range of the threshold for adverse effects for over a decade and
possibly longer (Figure 21.3). It is quite possible that DDT influenced lake trout fry survival in the Great
Lakes.
Toxaphene is another persistent pollutant that has been found to be elevated in lake trout from the
Great Lakes. Toxaphene was used primarily in the southern United States as an insecticide for cotton;
however, atmospheric transport of this insecticide mixture and subsequent condensation in the temperate
latitudes of the Great Lakes caused toxaphene to become elevated in lake trout of this region (Schmitt
et al., 1990). The concentration of toxaphene in lake trout from the Great Lakes ranged from 8 mg/kg
ww in the early 1980s to 0.1 to 2.0 mg/kg ww in the late 1980s (Gooch and Matsumura, 1985; Schmitt
et al., 1990) to concentrations of less than 1 mg/kg by the mid-1990s (Hickey et al., 2006). Adverse
effect thresholds of toxaphene toward reproduction and growth in fish have been estimated to be in the
range of 0.4 to 0.6 mg/kg (Eisler and Jacknow, 1985; Mayer et al., 1975). No threshold has been
established for adverse effects of toxaphene in lake trout. The concentrations of toxaphene in Great
Lakes salmonines may have exceeded the predicted threshold for adverse effects on reproduction and
growth during the 1980s and may well have been an additional stressor during this time.
Dietary exposure of fish to environmentally relevant concentrations of methylmercury can cause
negative effects on neuroendocrine function and reproductive performance. The effect of mercury on
steroid hormones and gonadal development was the focus of a recent study with tilapia (Oreochromis
niloticus). Tilapia exposed to methylmercury chloride (slow-release capsule, interperitoneally) resulted
in reduced steroid hormones and abnormal gonad development in females (Arnold, 2000). In another
study, steroid hormones (both 17β-estradiol and 11-ketotestosterone) were suppressed in both female
and male fathead minnows following a low dietary exposure to methylmercury (Drevnick and Sandhei-
nrich, 2003). The study found retarded gonad development in females that corresponded to a reduction
in 17β-estradiol and reduced spawning success. Thus, there is some evidence that methylmercury at
environmentally relevant concentrations (<1 µg/g in diets) can reduce steroid hormones, alter gonad
development, and impact spawning. The body burden of methylmercury that resulted in these impacts
was in the range of 3 to 5 µg/g ww in the whole fish (Drevnick and Sandheinrich, 2003). Chronic effects
on feeding behavior in grayling (Thymallus thymallus) were observed 3 years after a single acute exposure
to the developing eggs (Fjeld et al., 1998). Concentrations of methylmercury in the grayling greater than
0.27 µg/g egg ww were expected to result in reduced feeding efficiency (Fjeld et al., 1998). Concentra-
tions of methylmercury in Great Lakes lake trout were <0.3 µg/g whole carcass ww from 1976 to 1977
(May and McKinney, 1981) and <0.2 µg/g whole carcass ww in 1984 (Schmitt and Brumbaugh, 1990).
Even though methylmercury is a reproductive toxicant with known effects on the hypothalamus–pitu-
itary–gonad axis, the concentrations of methylmercury in Great Lakes salmonines over the last half of
the 20th century did not exceed reproductive thresholds for adverse effects and would not have been
expected to have contributed to the lack of recruitment observed in lake trout.
Polybrominated diphenyl ethers (PBDEs) have been used as flame retardants in plastics, clothes,
furniture, and numerous other consumer and industrial products over the past three decades (Hites, 2004).
Production of PBDEs in the United States is currently 200,000 metric tons per year (Hale et al., 2003).
The PBDEs used in plastics are not covalently linked to the plastic polymers and will leach out of the
plastics as the products age; consequently, PBDEs are one of the few halogenated, persistent chemicals