TOXICITY OF THE ANTISAPSTAIN FUNGICIDES, DDAC AND IPBC ...

4.5 TOXICITY OF DDAC AND IPBC TO FISHES AND AQUATIC INVERTEBRATES
Different species were tested at different acclimation temperatures, but no experiments specifically examined
the effect of temperature. Therefore, comments on the possible confounding effect of temperature are
not possible. However, all of the test temperatures used were relevant to water temperatures in the lower
Fraser River, except for the tests at 25 o C on Hyalella and Mysidopsis.
With regard to a possible confounding effect from the suspended sediment in the river, it is well established
that quaternary ammonium halides strongly adsorb to sediments. Lewis and Wee (1983), Lewis (1991),
Versteeg and Shorter (1992), and Szenasy et al. (1999) all demonstrated that DDAC was quickly adsorbed
to particulate matter in the Fraser River. While DDAC shows strong sorption properties, it is not known if
DDAC attached to particles can be toxic without first being released into solution. In a study by Qiao and
Farrell (1996) using Fraser River sediment, adsorption to sediment increased the uptake of hydrophobic
biphenyls across fish gills. The fact that DDAC has both hydrophilic and hydrophobic properties points to
the need to perform similar uptake experiments with DDAC.
While DDAC is highly adsorptive, IPBC is much less so. The observations in the Fraser River (Szenasy et al.
1999) suggest that IPBC is not adsorbed quickly to sediments in the immediate mixing zone. However, it
was detected in sediments of the Fraser, which suggests adsorption does occur over time. The first observation
indicates that the laboratory toxicity information is generally applicable to the immediate mixing zone,
while the second points to the need for sediment-bound toxicity testing.
Relevance of Acute Lethality For Deriving Water Quality Criteria
Acute toxicity tests are the first and often the only types of toxicity tests performed on new compounds.
Thus, acute toxicity values represent a large and useful comparative database from which water quality
guidelines are typically set. Similarly, our above predictions about protection of relevant Fraser River aquatic
organisms were based on the assumption that acute toxicity data are useful in this regard. Some of the work
performed here allows us to examine this assumption.
The relevance of acute lethality levels to the receiving environment hinges on the extent of the mixing zone
likely to have concentrations near these levels and the duration of time that these levels are maintained. In
the Fraser estuary, mixing of near shore discharges is strongly influenced by river flow rate and tidal stage.
Furthermore, many of the stormwater discharges from sawmills enter the river at the shore so the plume
tends to hug the shoreline, especially on an ebb tide (Hodgins et al. 1998). As many juvenile stages of fishes
and invertebrates utilize the near shore zone in the river, it is important to know these mixing characteristics
before the acute lethality data can be assessed. On the other hand, Szenasy et al. (1999), found that DDAC
concentrations declined even faster than the dilution rate and were below the detection limit (10 ppb) less
than 10 m downstream of the outfall.
Another aspect of acute lethality is the steepness of its onset. We consistently discovered unusually steep
concentration-response relationships for Bardac with fish and aquatic invertebrates (Fig. 1). The same occurred
for Polyphase with fish, but not with invertebrates. This steep concentration-response relationship is
in keeping with the more general finding for quaternary ammonium halides (Cooper 1988). One of the
implications of this relationship is that the concentrations for the NOEC and 100 per cent mortality were
rarely more than an order of magnitude apart. Thus, a 10-fold dilution from the LC 50 value would easily
prevent acute lethality and it also suggests that sublethal toxicity is less likely.
Novel information on the sublethal toxicity of antisapstains was generated in this study. The sublethal
exposure period was limited to 24 hours to better simulate a stormwater runoff situation. Test concentrations
were set at a proportion of the 96-h LC 50 value to assist comparisons. In general, a primary stress
response was not observed in either rainbow trout or starry flounder at an exposure concentration lower
than 50 per cent of the 96-h LC 50 value. Likewise, in unspecified studies with bluegill sunfish, coho
salmon, Daphnia magna and a mysid shrimp, the reported NOEC was always within 50 per cent of the
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