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4.6 ASSESSING THE POTENTIAL IMPACT OF THE ANTISAPSTAIN CHEMICALS DDAC AND IPBC with stronger current, calm water areas, such as sloughs, contain a higher ratio of silt and clay (Brewer et al. 1998; McLaren and Ren 1995). This study shows that DDAC in sediments, at sufficiently high concentrations, is bioavailable and toxic to benthic organisms and also to animals nearby in the water column. An important factor for assessing the relevance of this toxicity in the ambient environment is the persistence of DDAC in the sediment. This test found no degradation after 14 days at 23 o C. Consequently, since biodegradation is a temperature-dependent process, it may be assumed that DDAC in the Fraser River will likely persist longer than the 14-day duration of the bioassay as river temperatures are well below 23 o C most of the time. DDAC AND IPBC IN FRASER RIVER SEDIMENTS A preliminary survey of sediments in depositional zones located downstream of four lumber mills along the Fraser River was conducted on March 19, 1998. Duplicate sediment samples were analyzed for DDAC and IPBC and they were spiked with DDAC and IPBC to determine per cent recoveries. Recoveries ranged between 69 to 95 per cent for DDAC and 38 to 89 per cent for IPBC. (It is not clear why DDAC recovery was improved compared to previous results presented in this paper, which were from another laboratory; it could be related to minor differences in the organic phase-separation procedures used.) The concentrations of DDAC in the samples ranged from 0.52 to 1.26 μg/g with a mean of 0.91±0.29 μg/g dry weight (n=8). The concentrations of IPBC in the same samples ranged from 0.19 to 0.57 μg/g with a mean of 0.35 ±0.14 μg/g dry weight (n=8). The sediment composition was predominantly silt (over 60%) at three sites and sand (over 50%) at the fourth. The clay content ranged from nine to 30 per cent for the four sites. These levels were higher than anticipated, particularly for IPBC which has a half-life in aerobic soil of only two hours (Szenasy and Bailey 1996). In addition, the ratio of DDAC to IPBC used by the mills in B.C. is over 90:1 but the ratio measured in the sediment is only 2.5:1 (based on the mean values). This suggests that IPBC may be more persistent than expected in sediments or that there are other unaccounted-for sources of IPBC. Alternatively, DDAC may be more rapidly degraded than IPBC in these sediment environments. The levels of both chemicals were orders of magnitude higher than other pesticides measured in Fraser River sediments. By comparison, bed sediment levels of lindane—which exceeded federal sediment quality guidelines—in the North and Main arms had a maximum of only 0.00084 μg/g dry weight (Brewer et al. 1998). CONCLUSIONS AND RECOMMENDATIONS The recommended interim guideline for DDAC in water, for the protection of freshwater life, is 1.5 μg/L. This guideline value is based on the 48-hour LC value for Daphnia magna, a species not usually found in 50 the river. As 40- to 60-day-old sturgeon fry were found to be more sensitive to DDAC than D. magna, it is recommended that an independent toxicity test be conducted with sturgeon fry at a developmental stage that is likely to be exposed to DDAC in the upper estuarine reaches of the river. Such confirmatory test results should be available before ambient objectives for DDAC in the Fraser River are developed. During summer on an ebb tide, the zone of potential biological impact of DDAC in the plume below an outfall appears to be quite restricted. The concentrations fell below detection limits within ten metres or at slightly greater than 10:1 dilution in a survey when the effluent concentration was 60 per cent of the effluent guideline (700 μg/L). However, during different tidal and hydrological conditions, the concentration of DDAC in the river water may be higher. For example, higher concentrations of DDAC in water would be expected during slack tide and during periods with low suspended sediment content, such as in 76
4.6 ASSESSING THE POTENTIAL IMPACT OF THE ANTISAPSTAIN CHEMICALS DDAC AND IPBC winter. Also in winter, during low river flow, the chemical should be detected at greater distances downstream of the outfalls. Our assessment of the zone of potential biological impact was approximate because the analytical detection limit for DDAC in water was almost an order of magnitude above the interim guideline. Further, the analytical recovery results indicate that our measurements may be underestimating DDAC presence in the river. These factors hamper our ability to state conclusively that no biological impacts from DDAC would occur outside of the mixing zone. The recommended interim guideline for IPBC in water, for the protection of freshwater life, is 1.9 μg/L. The ambient concentrations of IPBC in the water column were not above detection limits during our limited survey, so our ambient assessment is inconclusive. However, it is quite likely that concentrations could be higher than the proposed draft guideline anywhere the plume does not achieve a dilution of greater than 63:1 if the runoff just meets the effluent guideline of 120 μg/L. This is predicted because the dilution experiments demonstrated that only about 10 per cent of the IPBC in the effluent-river mixtures adsorbed to particulates in river water and concentrations should be mostly dependant on the extent of mixing. Finally, there appears to be sufficient information for the development of ambient water quality objectives for IPBC in the Fraser River. Our survey of DDAC and IPBC in sediment deposition zones of the lower Fraser River found both DDAC and IBPC at relatively high levels. This result was expected for DDAC, but the detection of IPBC remains a mystery as it is thought to have a short half-life and we found only minimal adsorption to suspended sediments in river water during the dilution experiments. While the concentrations for DDAC were more than two orders of magnitude below the LOEL for the one invertebrate tested here, the lack of sediment toxicity tests for IPBC prevents any assessment of its possible effects. There is, as well, a possibility that the combined presence of both chemicals can result in synergistic effects on benthic organisms, as shown by Farrell and Kennedy (1999) in tests with Hyalella azteca. Our ability to assess potential impacts of either chemical on the benthic ecology of these depositional zones is hampered by the present lack of sediment quality guidelines. Such guideline development will require the determination of the half-life of both chemicals in aquatic sediments under the redox and temperature conditions encountered in the Fraser as both chemicals appear to have longer persistence than earlier laboratory studies would suggest. In conclusion, the bioavailability of DDAC and IPBC in deposition zones in the Fraser River and the Strait of Georgia should be further investigated to evaluate the ecological relevance of these observations. While many of the questions we set out to answer about the specific impacts of these chemicals in the Fraser River have not been resolved to our satisfaction, there were sufficient toxicity data produced during the course of our studies, other FRAP studies and industry-sponsored studies to generate interim guidelines for both chemicals in water. Accordingly, the present effluent criteria for DDAC and IPBC should be reevaluated in light of these new CCME guidelines. With present effluent criteria, dilutions of 466:1 and 63:1 are needed for DDAC and IPBC, respectively, to meet the new guidelines in the absence of any discharges upstream of a particular stormwater outfall. The toxicity of DDAC and IPBC in a marine receiving environment should also be evaluated. While it is argued that ionic complexation in seawater could reduce bioavailability of DDAC, the reduction in bioavailability due to adsorption to suspended sediment may not be a factor in the marine environment because TSS are typically low in these environments. The information gaps identified by this overview, the detection of both chemicals in sediments and their heavy usage in the lower Fraser River and coastal B.C. strongly suggest that these chemicals remain a concern for environmental management in the Fraser River Basin and the Georgia Basin. 77
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