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

4.6 ASSESSING THE POTENTIAL IMPACT OF THE ANTISAPSTAIN CHEMICALS DDAC AND IPBC 

69 

4.6 

ASSESSING THE POTENTIAL IMPACT OF THE 

ANTISAPSTAIN CHEMICALS DDAC AND IPBC 

IN THE FRASER RIVER 

by Erika Szenasy, ESB Consulting, Vancouver, BC 

Colin Gray, Aquatic and Atmospheric Sciences 

Division, Environment Canada, Vancouver, BC 

Dennis Konasewich 

Envirochem Services Ltd., North Vancouver, BC 

Graham van Aggelen and Vesna Furtula 

Pacific Environmental Science Centre 

Environment Canada, North Vancouver, BC 

and 

Lars Juergensen and Pierre-Yves Caux 

Guidelines Division, Environment Canada, Hull, Quebec 

Interim guideline levels for the protection of aquatic life were formulated for DDAC (didecyl dimethyl 

ammonium chloride) and IPBC (3-iodo-2-propynyl butyl carbamate) in water. This chapter summarizes 

the data used to establish these guidelines as well as preliminary toxicity data for DDAC in 

sediments. The measured and expected concentrations of these chemicals in water and sediments 

from the lower Fraser River are examined in terms of their potential threats to aquatic life. 

DDAC and IPBC are antisapstain chemicals used to prevent fungal growth on softwood lumber during 

transport to customers in Asia and Europe. DDAC is one of the most heavily used pesticides in the province. 

The quantity of antisapstain chemical formulations used by mills along the lower Fraser River was 680 

metric tonnes in 1996, the majority of which contained DDAC as the active ingredient. The actual amounts 

of DDAC and IPBC used were 155 and 11 metric tonnes, respectively. The majority of mills use the 

formulation NP1, a mixture of DDAC and IPBC. The second most common formulation is F2, containing 

DDAC and a borate salt (disodium octaborate tetrahydrate) as active ingredients (Redenbach 1997). Although 

much less IPBC is used than DDAC, its toxicity to aquatic organisms is similar to DDAC and the 

interaction of the two chemicals may produce synergistic effects in some organisms (Farrell and Kennedy 

1999). While 108 metric tonnes of borates were used, they are about 850 times less toxic to fish than 

DDAC and are considered to be of less concern in the Fraser Basin (Cavanagh 1995).


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


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).


IPBC is not considered a persistent substance because soil studies have found that degradation is rapid 

under aerobic conditions. Although there are no studies available for biodegradation in water, its behaviour 

is expected to be similar to that in soil. Its half-life in soil is two hours, producing the major degradation 

product, propargyl butyl carbamate (PBC), which in turn, has a half-life of 4.3 days. Carbamates are not 

generally considered persistent in water (Menzer 1991). In addition, PBC is 1,000 times less toxic than 

IPBC to both O. mykiss (80 mg/L versus 100 μg/l) and D. magna (60 mg/L versus 40 μg/L) (Springborn 

Laboratories Inc. 1992a, b). 

The most sensitive endpoint reported for fish was a 35-day LOEL of 19 μg/L for reduced weight and length 

of larval P. promelas exposed to IPBC as embryos (Springborn Laboratories Inc. 1992c). Toxicity levels 

ranged up to a 96-hour LC 50 of 1.90 mg/L in coho salmon embryo (Farrell and Kennedy 1999). 

Invertebrate toxicity ranged from a 48-hour LC 50 of 40 μg/L for adult D. magna (Farrell and Kennedy 

1999) to a 24-hour LC 50 of 1.42 mg/L for D. magna juveniles less than 24-hours old (Inveresk Research 

International 1989). 

DDAC AND IPBC CONCENTRATIONS IN FRASER RIVER WATER 

The survey of DDAC and IPBC in the Fraser River was divided into two components, a plume dispersion 

study and an on-site dilution study. The objective of the plume dispersion study was to determine the 

concentrations of DDAC in the effluent plume from the mill outfall as it dispersed in the river during a 

rainstorm event. The purpose of the dilution study was to investigate the partitioning of the two chemicals—when 

released during a rainfall event—between river water and suspended sediment. 

The survey was undertaken between April and August 1997 during rainfall events. Sampling was conducted 

downstream of stormwater discharges at selected sawmills in the Vancouver area. Two types of mills 

were sampled, those using the F2 (DDAC/borate) formulation and others using the NP1 (DDAC/IPBC) 

formulation. As the survey was conducted during a period of relatively high flow and suspended sediment 

content, the results are applicable to those river conditions. Further, because the overseas lumber market 

demand had declined during this period and less wood was being treated, the volume of chemicals used 

wasn’t representative of typical volumes used. 

Methodology details are described in Szenasy et al. (1999). 

Results 

Plume dispersion study 

At the F2 mill site on May 27, the effluent contained an average of 446 μg/L DDAC, of which approximately 

half was in the decanted fraction (water with most of the solids removed). In the river, five metres 

from the outfall, total DDAC was at the analytical detection limit of 10 μg/L. Boron was an adequately 

conservative element which remained in the decanted fraction and hence was used to trace the plume in the 

river and to calculate DDAC recovery. DDAC recovery decreased more rapidly with distance from the 

outfall than boron. The boron concentrations indicated that the plume had mixed to greater than a 10:1 

dilution within 10 m. Results are summarized in Table 2 (see end of chapter) and the dilution of DDAC 

and boron in the plume, relative to distance from the discharge, are shown in Figure 1. These results show 

that DDAC readily associates with particulate matter (about half the detectable DDAC appears to be in the 

particulate phase) and the dilution capacity of the Fraser River is very high in the summer months. 

The total suspended solids (TSS) concentration in the plume increased almost four-fold (relative to both 

the plume and the river water upstream [TSS of river water=142 mg/L]) at a distance of about four metres 

from the outfall (Table 2). While some of this increase could be due to flocculation (Krishnappan and 

72


Lawrence 1999) and thus increased 

recovery of TSS, it is more likely that 

the force of the stormwater discharge 

resuspended bottom sediments in the 

shallow near-shore zone. This process 

would provide more particulate 

adsorption sites for DDAC. 

On-site dilution study 

The partitioning of the chemicals between 

suspended sediment and water 

was evaluated by diluting effluent 

containing DDAC or DDAC and 

IPBC with known volumes of river 

water. This study also assessed analytical 

recovery of the chemicals in 

total water samples (containing both 

suspended sediment and water) and 

decanted samples. 

Less than 50 per cent of the DDAC 

in stormwater runoff from the mill 

using F2 was in the decanted fraction 

(Table 3 [see end of chapter], 

Fig. 2). The proportion of recovered 

DDAC in the decanted fraction, after 

mixing with river water, remained 

between one-third and one-half of 

the total. This finding is not surprising 

considering the relatively high 

level of suspended solids in the runoff 

and the highly adsorptive character 

of this chemical. 

As in the plume samples, the TSS values 

in the dilution mixtures were 

higher than in either component. In 

this case only flocculation, which 

could have led to greater recovery of 

the filterable total suspended solids 

in the mixtures, is available as an explanation. 

Figure 1. Concentration of DDAC and boron in the Fraser River at 

distances downstream of the F2 mill stormwater discharge. 

Figure 2. The effect of river water on DDAC and boron recovery 

from F2 mill stormwater effluent. Per cent recovery is relative to 

undiluted effluent. 

Perhaps the most important observation from these dilution experiments was that the analytical recovery of 

DDAC was very poor. In both the total and decanted fractions only from 28 to 50 per cent of the expected 

level was recovered. As well, recovery was less in the 25 per cent effluent mixture than in the 50 per cent 

mixture and there was a tendency for less recovery from the decanted fraction than the total. These observations 

could be the result of strong and irreversible adsorption of the chemical in the dissolved fraction to 

river-borne particles, as well as the flocculation of particles from both sources which made extraction of 

DDAC originally adsorbed onto effluent particles more difficult. There is a good possibility, however, that 

73


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


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


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


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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80 

Table 2. Concentrations and recovery of DDAC, boron and total suspended solids (TSS) in stormwater effluent from the F2 mill and in the effluent 

plume within the Fraser River in the plume dispersion study. 

SAMPLE 

100% effluent 

1 m 

5 m 

10 m 

* Average value (n=2) 

DDAC 

BORON 

CONCENTRATION (μg/L) 

% RECOVERY RELATIVE TO 

UNDILUTED EFFLUENT 


% RECOVERY RELATIVE 

TO UNDILUTED EFFLUENT 

TOTAL DECANTED TOTAL DECANTED TOTAL DECANTED TOTAL DECANTED 

446* 

111.5* 

11 

81 

Table 4. Concentrations and recovery of DDAC and IPBC from a laboratory dilution study using spiked effluent from an NP1 mill site diluted with 

Fraser River water. 

SAMPLE 

(RATIO OF 

EFFLUENT: 

RIVER WATER) 

Original effluent a 

100:0 b 

50:50 

25:75 

10:90 

River water 

DDAC 

IPBC 


% RECOVERY OF EXPECTED 

CONCENTRATION 


% RECOVERY OF EXPECTED 

CONCENTRATION 

TOTAL DECANTED TOTAL DECANTED TOTAL DECANTED TOTAL DECANTED 

35 

1039* 

231* 

61 

13

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