assessing the potential impact of the antisapstain chemicals ddac ...

More documents

Recommendations

Info

4.6 ASSESSING THE POTENTIAL IMPACT OF THE ANTISAPSTAIN CHEMICALS DDAC AND IPBC the analytical techniques used to date may not be effective at analyzing these target chemicals in these complex mixtures of wood particles, clays and surfactants (Boethling and Lynch 1992; BC Research 1991). Until the analytical difficulties are overcome and further controlled experiments are conducted, it is impossible to assess whether the lack of analytical recovery is also indicative of biological unavailability. Since the sampled effluent from the NP1 mill did not contain sufficient DDAC or IPBC for detection in the mixing zone, the effluent was spiked with NP1 to assess the chemicals’ behaviour in a dilution series mimicking a mixing zone. NP1 was added to the effluent to produce concentrations of 1400 μg/L DDAC and 100 μg/L IPBC (assuming no DDAC or IPBC was in the original effluent). The river water used in this test was marginally lower in suspended sediment content (126 mg/L) than the river water used in the F2 study (142 mg/L). The results are shown in Table 4 (see end of chapter) and in Figure 3. A little more than 10 per cent of the spiked IPBC was not recovered from the effluent or subsequent dilutions with river water and slightly greater amounts were not recovered in decanted fractions. Almost 30 per cent of the spiked DDAC was not recovered from the effluent and recoveries in mixtures became progressively less as the percentage of river water increased. As the TSS content of the effluent was a relatively low 32 mg/L, much of the calculated loss in the 100 per cent effluent could be due to an already mentioned analytical limitation. SEDIMENT TOXICITY TESTS WITH DDAC Sediment toxicity bioassays were conducted with DDAC to assess the chemical’s bioavailability and toxicity to aquatic organisms. The tests were conducted using a bulk sediment sample from the upper Fraser Basin, to which DDAC was added. To investigate the route of DDAC exposure from contaminated sediment to organisms, the following tests were employed: Hyalella azteca was used to assess toxicity to benthic invertebrates; Daphnia magna was used to determine if DDAC in the sediment was bioavailable and toxic to organisms in the overlying water; and a solid phase Microtox® test was used to determine if the chemical was available to organisms directly from the sediment. Acute and chronic toxicity of DDAC in spiked sediment was tested with the freshwater amphipod, Hyalella azteca. The 14-day LC 50 was 1,100 μg/g Figure 3. The effect of river water on DDAC and IPBC recovery from NP1 mill stormwater effluent spiked with 1400 μg/L DDAC and 100 μg/L IPBC. DDAC with a steep dose-response (Fig. 4). The NOEL (no-observable-effect level) was 750 μg/g and the LOEL was 1,000 μg/g. Our acute toxicity results are similar to those observed by TRS in a 28-day sediment toxicity study with Chironomis tentans (TRS 1997). A concurrent 14-day bioassay was conducted with D. magna neonates exposed to the same spiked sediment. Based on sediment concentrations, the 14-day LC 50 was 2,250 μg/g, with a NOEL value of 1,500 74
4.6 ASSESSING THE POTENTIAL IMPACT OF THE ANTISAPSTAIN CHEMICALS DDAC AND IPBC μg/g and a LOEL value of 3,000 μg/g. The LC 50 based on exposure concentrations from the water was 1,033 μg/L. The NOEL was 456 μg/L and the LOEL was 1,609.5 μg/L. There was no observed effect on reproduction. This observed LC 50 was 10 to 20 times higher than LC 50 s using standard laboratory water in the absence of sediment. This result is similar to the water column toxicity tests undertaken by TRS (1997) in tanks containing a layer of Fraser River sediment, which demonstrated a 13-fold decrease in toxicity to juvenile sturgeon. Other studies with daphnids found 48 hour LC 50 values ranged from 37 to 94 μg/L with a NOEL as low as 30 μg/L (Farrell and Kennedy 1999; TRS 1997). The manufacturer’s studies conducted with DDAC and Fraser River water found a NOEL of 375 μg/L for Ceriodaphnia dubia (7 day test; TRS 1997), which is similar to the Figure 4. Dose-response curves of the benthic amphipod, Hyalella azteca, the crustacean, Daphnia magna and the luminescent bacteria Vibrio fisheri (solid phase Microtox®) to Fraser Basin sediments spiked with DDAC from a 14-day sediment toxicity bioassay. The response of H. azteca and D. magna is expressed as per cent mortality. The response of Microtox® is expressed as per cent IC 50 (per cent of DDAC contaminated sediment in sample which causes 50% inhibition in light emission from the bacteria). NOEL of 456 μg/L for Daphnia from this study. The difference between response in laboratory dilution water and site water or laboratory water with sediment present is most likely due to adsorption of DDAC to particles suspended in the overlying water; thus rendering the measured DDAC unavailable to organisms. The Microtox® solid-phase test results indicate that sediment spiked with a DDAC concentration of 1,500 μg/g or greater was toxic to the bacteria. Concentrations of 1,000 μg DDAC/g sediment or less were nontoxic to the bacteria. The effect of DDAC concentration on IC 50 values is shown in Figure 4. At each concentration, test results for Days 0, 7 and 14 were similar. DDAC was stable for the duration of the study with minimal degradation in the sediment. The concentration range was 375 to 6,000 μg/g. Average recoveries from sediment ranged from 72 to 110 per cent for all concentrations. Levels of DDAC in the water were highest on Day 0. Concentrations ranged from 261 μg/L (Day 0, sediment concentration of 750 μg/g) to 2,959 μg/L (Day 0, sediment concentration of 6,000 μg/g). DDAC concentration in water was below the analytical detection limit at exposure concentrations of 375 and 500 μg/g. In general, the amount of DDAC in the water column did not exceed 0.05 per cent of sediment levels. The sediment available for testing consisted of 77 per cent sand, 16 per cent silt and 6.4 per cent clay. The relatively high silt and sand content and low clay content of the sediment should favour the bioavailability and recovery of DDAC since clays are known to bind DDAC more strongly (TRS 1997). While the composition of bed sediments in lower Fraser River depositional zones is predominantly sand and silt in areas 75
Page 1 and 2: 4.6 ASSESSING THE POTENTIAL IMPACT
Page 5: 4.6 ASSESSING THE POTENTIAL IMPACT
Page 13: 81 Table 4. Concentrations and reco

assessing the potential impact of the antisapstain chemicals ddac ...

Create successful ePaper yourself

Delete template?

Save as template?