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

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4.5 TOXICITY OF DDAC AND IPBC TO FISHES AND AQUATIC INVERTEBRATES and fishes (Cooper 1988). However, we have either identified some of the more sensitive aquatic organisms, or Bardac is one of the more acutely toxic quaternary ammonium compounds. For Polyphase, again there is consistency between our acute toxicity data and the proprietary information. Henderson (1992b) reported LC 50 values for rainbow trout that ranged Table 3. Acute (96-h exposure) toxicity of a mixture (1:8) of Polyphase P-100 and Bardac 2280 to fishes and invertebrates. TEST SPECIES EXPOSURE DURATION Fishes: Coho 96-h alevin (53-day old) Coho 96-h juvenile (7-month old) Rainbow trout 96-h juvenile Starry Flounder 96-h juvenile Invertebrates: Hyalella azteca 48-h Daphnia magna Neomysis mercedis 48-h 48-h from 67 ppb IPBC for a 24-h flow-through bioassay to 310 ppb IPBC for an unspecified bioassay. In our study, after converting to active ingredient concentrations, juvenile rainbow trout and coho fry had 96-h LC 50 values of 97 and 126 ppb, respectively. Henderson (1992b) also reported that rainbow trout were about two times more sensitive to IPBC than bluegill sunfish. We found that rainbow trout (and coho salmon) were almost four times more sensitive to IPBC than starry flounder. Invertebrates represented the most sensitive species (D. magna; LC 50 value of 39 ppb) and the most tolerant species (N. mercedis; LC 50 value of 2,832 ppb). In contrast to our findings, Henderson (1992b) reported a 48-h LC 50 value for D. magna (645 ppb) that was almost 15 times higher than the value obtained here. The minimum data requirements for setting Canadian water quality guidelines for both chemicals are met with the proprietary data and this study (Environment Canada 1998; 1999). The recommended interim guidelines were set at 1.5 and 1.9 ppb for DDAC and IPBC, respectively. It is important to discuss the relevance of acute toxicity testing on standard test organisms, upon which the guidelines are based, to the toxicity potentially experienced by species living in the Fraser and its specific receiving environment conditions. The following discussion focuses on potential toxicity impacts of stormwater discharges on resident species, including considerations of the influence of receiving environment conditions and the significance of sublethal exposure. Relevant Species The test species that were relevant to the lower Fraser River and its estuary included N. mercedis, starry flounder, juvenile coho salmon and juvenile white sturgeon. Under the present regulatory limit of 700 ppb DDAC for stormwater discharge and using 50 per cent lethality as the measure of a deleterious effect, the most tolerant of the invertebrate or fish species we tested (i.e. adult N. mercedis and juvenile starry flounder) are presumably protected as dilution would further reduce exposure concentrations. However, since these animals were collected in the estuarine area of the Fraser River, where they normally live and breed, it could be argued that our testing used only a selected sub-population already exposed to, and tolerant of, numerous toxicants that potentially included DDAC. 62 NOEC 320 ppb 320 ppb 320 ppb 700 ppb 14 ppb 1,500 ppb 72 ppb 160 ppb 1,400 ppb ADDITIVE INDEX (95% CI) -0.37 (-0.39 to -0.33) -0.27 (-0.33 to -0.17) -0.38 (-0.52 to -0.24) 0.06 7.47 (8.34 to 29.4) -1.77 (-2.32 to -1.37) 0.37 (0.20 to 0.39) Nominal concentrations of the formulation (8 parts Bardac 2280 and 1 part Polyphase P-100) are presented. Nominal concentrations of the active ingredients can be calculated using 0.71 times the formulation concentration for DDAC and 0.065 times the formulation concentration for IPBC.
4.5 TOXICITY OF DDAC AND IPBC TO FISHES AND AQUATIC INVERTEBRATES Our studies suggest that, if exposed for sufficient time at the 700 ppb level, juvenile coho, and especially juvenile white sturgeon, would not be adequately protected by the regulatory limit for DDAC. It is important, therefore, to determine the likelihood of their exposure to DDAC and at what levels (see Szenasy et al. 1999). It is also salient to evaluate whether or not the higher sensitivity of these species is characteristic of other aquatic organisms that were not tested here, but nonetheless at risk of DDAC exposure. The extreme sensitivity of 40-day-old juvenile white sturgeon found in our study is of particular concern. While recent testing done at another lab has found the sensitivity of white sturgeon to be similar to rainbow trout (TRS 1997), that lab tested 80-day-old juveniles, and it may be that sturgeon could be more vulnerable at the very early life stages. The water quality characteristics also likely differed between the two test locations. In addition, both the TRS (1997) and our study utilized a Sacramento River, rather than a Fraser River, fish stock, which makes their applicability less certain. Unfortunately, this problem will not be alleviated soon because there is no immediate supply of fertilized Fraser white sturgeon eggs. Once a supply is developed, toxicity tests should be done in another independent lab to investigate the range of toxicity shown at several ages, including the ages tested so far. Of equal importance, there is an urgent need to describe the ecology of white sturgeon in the Fraser River to identify their probability of exposure, particularly to the early life stages. White sturgeon populations in the Fraser River have been reduced dramatically through over-harvesting. Their recovery depends on eliminating contaminant stress as well as harvesting, which is already banned. Under the present regulatory limit of 120 ppb IPBC and using 50 per cent lethality as the measure of a deleterious effect, the most tolerant of the invertebrate or fish species we tested (i.e. N. mercedis and juvenile starry flounder) appear to be protected. Protection of juvenile coho, if exposed for sufficient time at this level, would be marginal. Measured IPBC concentrations in stormwater runoff from sawmills on the lower Fraser River have ranged from non-detectable to as high as 370 ppb, whereas DDAC has been measured at levels as high as 6,000 ppb (Envirochem 1992). However, recent improvements in the handling of treated lumber have reduced the concentrations in stormwater runoff to levels consistently at or below the effluent guidelines (Environment Canada 1997). The likelihood of biota being exposed to these guideline levels, which are in the range of the LC 50 values, depends on the extent of dilution, degradation and adsorption onto particulate matter in the plume as it mixes with river water. These factors are discussed below. Relevance of Laboratory Toxicity to the Field When extrapolating toxicity data obtained in dechlorinated municipal tap water to conditions in actual river water, it is important that specific differences in water quality are assessed. In the case of the Fraser River, especially in the lower estuarine reaches, the temperature, salinity and turbidity are highly variable. Furthermore the mixing of a stormwater discharge is dependent on river flow and tidal cycles, both of which vary considerably. Ideally, toxicity testing could be undertaken in mesocosms (see Culp et al. 1999) containing some of the more sensitive species in conditions more like the river. Unfortunately, the mesocosm approach is at an early stage of development and was not applied in this study. The following discussion, then, focuses on the potential influence of salinity, temperature and suspended sediments on acute toxicity levels that can be suggested based on the study presented here. In the case of salinity, no significant change in toxicity to Bardac was observed with coho smolts. LC 50 values were 950, 950 and 850 ppb for seawater salinities of 0, 15, and 30‰, respectively. It is also noteworthy that the two euryhaline species (starry flounder and N. mercedis) which were tested in salt water had the highest tolerance to Bardac of the fish and invertebrates tested. These observations suggest that species that can adjust to variable salinity regimes may be relatively tolerant to this compound. 63
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