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4.6 ASSESSING THE POTENTIAL IMPACT OF THE ANTISAPSTAIN CHEMICALS DDAC AND IPBC DDAC is a cationic surfactant that belongs to a group of chemicals known as quaternary ammonium compounds (QACs). QACs are commonly used in industry as disinfectants and more recently as a molluscicide to control zebra mussels (TRS 1997; Schoenig, pers. comm. 1997). The mode of action of DDAC is cellular membrane disruption, causing damage to exposed areas in animals (such as gills and digestive tracts) (Wood et al. 1996; Henderson 1992). DDAC is toxic to aquatic organisms, both fish and invertebrates, causing death (Bennett and Farrell 1998; Farrell and Kennedy 1999; Wood et al. 1996). IPBC is a carbamate compound. The mode of action in animals is typically acetylcholinesterase inhibition (Ecobichon 1991); however, the specific behaviour of IPBC is unknown. In fungi, the mode of action is associated with iodine toxicity (Ward, pers. comm. 1997). IPBC is also toxic to aquatic invertebrates and fish (Farrell and Kennedy 1999). A portion of the chemicals applied to wood ends up being released to the environment during rainy weather when precipitation washes the chemicals off treated lumber stored in the open or from equipment used to move the lumber around the site. Levels of DDAC and IPBC in the runoff or effluent are regulated by the BC Ministry of Environment, Lands and Parks (BCMELP). The current effluent criteria in B.C. for DDAC and IPBC are 700 μg/L and 120 μg/L, respectively (Government of British Columbia 1990). These effluent criteria are based on standard toxicity tests using rainbow trout, whereas receiving water or ambient guidelines are set after testing two fish and invertebrate species and one algae or vascular plant species. Other factors considered in deriving ambient guidelines are the relative stability of the chemical in the environment and its bioconcentration potential. When developed, ambient guidelines can be used to evaluate the overall effectiveness of the effluent criteria in ensuring safe levels outside of mixing zones. A broader assessment of potential impacts was possible in our program because new information on the toxicity of the chemicals to fish and invertebrates important to the Fraser estuary was developed in a Fraser River Action Plan (FRAP)-supported research project (Bennett and Farrell 1998; Wood et al. 1996; Farrell and Kennedy 1999). Our assessment also used new information on dissolved and particulate concentrations of the chemicals encountered in the river during runoff events, the chemicals’ interaction with suspended sediments in mixtures of effluent and river water, and the toxicity of DDAC to benthic organisms. DEVELOPMENT OF CANADIAN WATER QUALITY GUIDELINES FOR DDAC AND IPBC Canadian Water Quality Guidelines (WQGs) are designed to protect freshwater organisms in the ambient receiving environment. They are developed by the federal government (Guidelines and Standards Division, Environment Canada) under the auspices of the Canadian Council of Ministers of the Environment (CCME). Although these recommended benchmarks are not enforceable by law, they are used by other levels of government as the scientific basis for site-specific objectives that, in turn, are used to develop standards, criteria or discharge limits, which can be legally enforceable. In order to develop WQGs, a toxicological and environmental fate database on each chemical is compiled from all sources, including the peer-reviewed literature and, in some cases, voluntary submissions from the chemical manufacturer. Testing species for which standardized protocols exist (e.g. Environment Canada, US Environmental Protection Agency [USEPA] and American Standards for Testing and Materials [ASTM]) are preferred for guideline development, however test results obtained using ecologically-relevant species with experimental protocols are also considered. The main sources of data for DDAC and IPBC interim guideline development were FRAP-sponsored toxicological research (Bennett and Farrell 1998; Wood et al. 1996; Farrell and Kennedy 1999) and industry data from the manufacturers of DDAC (Lonza, Inc.) and IPBC (Troy Corpo- 70
4.6 ASSESSING THE POTENTIAL IMPACT OF THE ANTISAPSTAIN CHEMICALS DDAC AND IPBC ration). The information available was sufficient for setting interim guidelines; full guidelines would require more chronic toxicity testing. DDAC Toxicology and Interim Guideline The interim guideline for DDAC, derived according to the CCME protocol (CCME 1991), was calculated by multiplying the most sensitive accepted endpoint value by a safety factor of 0.05 (Environment Canada 1998; Table 1). This safety factor is used when the chemical is assumed to be non-persistent and only acute toxicity data are available. The 48-hour LC (lethal concentration at which 50% of organisms die) value of 50 30 μg/L for the water flea, Daphnia magna, was selected as the most defensible sensitive endpoint value (Farrell et al. 1998). The calculation yielded a recommended interim guideline value of 1.5 μg/L. Table 1. Value of interim Canadian water quality guideline for DDAC and IPBC. PARAMETER DDAC IPBC GUIDELINE VALUE (μg/L) 1.5 1.9 1. lowest observed effect level Reference: Environment Canada 1998; 1999 CRITICAL VALUE (μg/L) 30 19 71 SAFETY FACTOR 0.05 0.1 TEST ORGANISM 48-h LC 50 35-d LOEL 1 Daphnia magna (water flea) Pimephales promelas (fathead minnow) Invertebrate toxicity varies widely, from the chemical’s guideline critical value, a 48-hour LC 50 of 30 μg/L for D. magna, to a 48-hour LC 50 of 6.12 mg/L of active ingredient for the mussel, Obliquaria refexa (Waller et al. 1993). Fish toxicity data ranged up to a 96-hour LC 50 of 2.81 mg/L for Oncorhynchus mykiss (rainbow trout) (Liu 1990 in Henderson 1992). Sturgeon fry at 40- to 60-days old were much more sensitive to DDAC than any other species tested (Bennett and Farrell 1998). The 96-hour LC 50 is between 1.0 and 10 µg/L for these fry. This is one to two orders of magnitude lower than the next lowest-observed-effect level (LOEL) for fish, a 24-hour LOEL of 100 µg/L for the swimming performance of O. mykiss (Wood et al. 1996). In the tests with sturgeon, toxicity generally decreased with increasing age and size of the fish. This was confirmed in a subsequent study on sturgeon, when TRS (1997) found that the LC 50 for 80-day-old fry had increased to over 400 ug/L, which is typical of the life stages tested in other species. The younger sturgeon larval/fry results were not used for the interim guideline derivation because the study was exploratory in nature and was not conducted according to standardized toxicological test methods. However, their study has raised concerns regarding sturgeon larval/fry sensitivity to DDAC and this sensitivity should be re-tested. Two other species present in the Fraser estuary, mysid shrimp (Neomysis) and starry flounder (Plathicthys stellatus), were also tested. In general, these two species were less sensitive to DDAC, as well as IPBC, than the freshwater organisms (Farrell and Kennedy 1999). IPBC Toxicology and Interim Guideline The interim guideline for IPBC was derived by multiplying the 35-day LOEL for Pimephales promelas (fathead minnow), 19 μg/L (Springborn Laboratories Inc. 1992c), by a safety factor of 0.1. This safety factor is recommended by CCME (1991) when the chemical is assumed to be non-persistent and the available end-point is based on a chronic toxicity test. This yielded a recommended interim guideline value of 1.9 μg/L (Environment Canada 1999; Table 1).
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