Chlorophenols in freshwater and marine water

​​​Toxicant default guideline values for protecting aquatic ecosystems

October 2000

Description of chemical

The solubility of chlorophenols decreases with increased chlorine substitution and decreased pH. Pentachlorophenol (PCP) is readily soluble at 8 g/L at pH 8 (20°C), 2 g/L at pH7 but only 0.14 g/L at pH 5 (Hobbs et al. 1993).

The mono-chlorophenols (mono-CPs) are used as antiseptics, disinfectants, medicines and veterinary products, as chemical intermediates for the manufacture of higher chlorophenols, catechols and dyes, and as soil sterilants. 4-CP is used as a denaturant for alcohol. Of the 10 isomers of dichlorophenols, only 2,4-DCP has been used most extensively for manufacture of the herbicide 2,4-D. Trichlorophenols are used as fungicides, disinfectants (e.g. hexachlorophene), bacteriacides, preservatives in adhesives, textiles, rubber and other materials and for water treatment in cooling towers and paper mills. 2,4,5-TCP is also used for manufacture of the herbicide 2,4,5-T. 2,3,4,6-TeCP is used in conjunction with PCP as a timber preservative.

PCP is used as biocide, disinfectant, and pesticide/herbicide (CCREM 1987) and has been commonly used as a timber preservative against fungal attack, e.g. mushroom boxes and telegraph poles. It has also been used in the processing of paints, leather and fabric (CCREM 1987). The uses of PCP are restricted in most countries (Hobbs et al. 1993) including Australia and New Zealand, and environmental concentrations should decrease in many locations. It is registered as a pesticide in Australia (NRA 1997a) against timber decay, borer, fungus and sapstain and for interior treatment of boats and trailers. Chlorophenols have been commonly found in chlorinated effluents, including pulp mill effluents (CCREM 1987) and sewage plants (Pablo et al. 1997).

Fate in the environment

Chlorophenols may evaporate from water, adsorb on sediment, photolyse readily near the water surface and biodegrade. Complete removal of 2-CP and 4-CP occurred in 13 to 36 days, although 3-CP was more persistent (HSDB 1996). Half-lives in sediment for 4-CP and 2,4,5-T were 20–23 days at 20°C (HSDB 1996). Volatility and biodegradation rates decrease with increasing chlorine substitution, but potential to adsorb to sediment increases. 2,4,5-TCP also oxidises to form a quinone (HSDB 1996).

PCP was detected in snow and rain samples in Canada (NRCC 1982) and Finland (Paasivirta et al. 1985). The main mechanism for removal of PCP from surface waters is biodegradation (CCREM 1987). Reductive dechlorination of PCP leads to less toxic tetra- and trichlorophenols (Wong & Crosby 1981). Most aquatic studies suggest a half-life for PCP of 100 days, with higher temperatures and aerobic conditions increasing the breakdown (CCREM 1987). PCP may persist for longer in sediments. The current analytical practical quantitation limit (PQL) for 2-CP, 4-CP, 2,4-DCP, 2,4,6-TCP and 2,3,4,5-TeCP is 2 polychlorinated biphenylspolychlorinated biphenyls µg/L (NSW EPA 2000). The practical quantitation limit (PQL) for PCP is 4 µg/L.

Bioaccumulation

More highly chlorinated phenols would be expected to bioaccumulate in aquatic organisms to a greater extent than mono- and di-chlorophenols (2,4,5-TCP has a log K_ow of 4.1 and PCP up to 4.8, depending on pH). Fathead minnows Pimephales promelas exposed to radiolabelled 2,4,5-TCP at two concentrations (4.8 and 49.3 µg/L) showed bioconcentration factors around 1800 (Call et al. 1980). Bioconcentration factors (BFs) of between 60 and 5000 have been reported for PCP for invertebrates and 200 and 15,000 for fish (Niimi & McFadden 1982, Fox & Joshi 1984). Although uptake from water is relatively rapid, depuration is also rapid; the estimated biological half-life of PCP in trout was less than 7 days (Niimi & Cho 1983). Chlorophenols impair the taste of fish and shellfish at concentrations below those which cause toxic effects (USEPA 1979b). Many overseas guidelines for chlorophenols are set at levels to minimise tainting of fish flesh. Canada (CCREM 1987) adopted guidelines at 0.5 of the threshold for tainting (flavour impairment) reported by Shumway and Palensky (1973). These tainting thresholds are 15 µg/L for mono CP, 0.4 µg/L for DCP (the most critical isomer for tainting) and 36 µg/L for triCP (2,4,6-TCP is 52 µg/L). Detailed figures to protect against tainting of fish flesh (0.5 of the tainting threshold) for isomers of mono- and di-chlorophenols are also reported in Table 8.3.21. If tainting of fish flesh is an issue at the site under study, users may prefer to apply these figures instead of the figures that are meant to protect aquatic ecosystems. Tainting thresholds are lower than the trigger values for 2-CP, 4-CP, 2,4-DCP and 2,6-DCP but appear to be above the aquatic ecosystem protection levels for other phenols (where tainting values are known), at least at 95% protection.

Jarvinen and Ankley (1999) report data on tissue residues and effects for pentachlorophenol for 8 freshwater species and four marine species. It is not possible to summarise the data here but readers are referred to that publication for more information. Some data are also available for other chlorophenols.

Aquatic toxicology

Data from short-term tests considered for guideline derivation are detailed in Table 8.3.21 for mono- and dichlorophenols, and in Table 8.3.22 for tri- and tetrachlorophenols and PCP. These are acute data for fish and invertebrates and chronic EC50 (growth) for algae and ciliates. Chronic invertebrate and fish NOEC data are outlined below.

2-chlorophenol

Freshwater cladoceran: reproductive impairment NOEC (24 d) for Daphnia magna of 300 µg/L. The 95% protection level (derived from acute data) was above this and it is recommended that the 99% protection level be used for slightly to moderately disturbed systems. No ACR was available and the default acute-to-chronic ratio (ACR) of 10 was used. Even the 99% level is slightly above the chronic NOEC. If users are concerned about similar species, the trigger value (99%) could be divided by a factor of 1.5 to give a value of 230 µg/L. This lower value is recommended for high conservation systems in the absence of other data.

4-chlorophenol

Freshwater fish: Chronic growth and mortality NOEC for one species of 249 µg/L.

Freshwater crustacean: Chronic NOEC (mortality) for two species of cladocerans (10-11 d), 200 to 2600 µg/L and for reproductive impairment for the same species of 630 to 1600 µg/L. The lowest figure was for Ceriodaphnia dubia (10-d mortality) but other end-points for this species were 1600-6000 µg/L.

Although an ACR of 5.74 was available, the default ACR of 10 was used to protect these species from chronic toxicity.

2,4-dichlorophenol

Freshwater fish: Chronic 85-d NOEC for Oncorhynchus mykiss growth of 179 µg/L (45 d of 560 µg/L) and for mortality between 99 µg/L (100 days) and 179 µg/L.

Freshwater crustacean: Chronic 21-d NOEC (reproductive impairment) to D. magna, 210 µg/L.

To provide adequate protection for D. magna and O. mykiss or equivalent species, the 99% protection level (120 µg/L) should be adopted for slightly to moderately disturbed systems.

2,4,5-trichlorophenol

Freshwater fish: Chronic 7-d NOEC (ELS growth of Pimephales promelas) of 360 µg/L.

2,3,4,6-tetrachlorophenol

Freshwater crustaceans: 7-d NOEC, four species, 240-340 µg/L. Although the lowest acute toxicity for D. magna is reported as 90 µg/L, the geometric mean is 295 µg/L.

Freshwater rotifers: 7-d NOEC, two species, 200-220 µg/L.

To provide an adequate margin of safety for acute toxicity to D. magna or equivalent species, the 99% protection level (10 µg/L) should be adopted for slightly to moderately disturbed systems. This chemical has the potential to bioaccumulate and hence the 99% protection level is recommended as a precautionary measure for this reason also.

Pentachlorophenol

There were acute freshwater data for PCP on 84 freshwater species from nine taxonomic groups and chronic data for 11 species from four groups. For marine systems, there were acute data for PCP on 30 species from eight taxonomic groups.

Freshwater fish: 28-d NOECs for P. promelas of 45 µg/L (growth), 73 µg/L (mortality) and 128 µg/L (hatching); 45-d NOEC (mortality) for Micropterus salmoides of 41 µg/L; 21 d (mortality) Oryzias latipes of 271 µg/L. Although the lowest acute LC50 was 18 µg/L (O. mykiss), the geometric mean for this species was 285 µg/L. The next lowest figures were 38 µg/LC (Leuciscus rutilus roach), 40 µg/L (Coregonus muksun whitefish), and 45 µg/L (Esox lucius northern pike).

Freshwater crustaceans: 13-21-d NOECs for four species of cladocerans, (reproduction and mortality), 50-320 µg/L. Crayfish, 8-d LC50 of 3000–5500 µg/L.

Freshwater algae: 96-h algal growth two species 9000-53,000 µg/L.

Marine invertebrates: 48-h EC50 for echinoderm growth, 710–870 µg/L; oyster 12-d LC50 71 µg/L.

An ACR of 4.54 was used for calculation of the marine trigger value.

Australian and New Zealand toxicity data

4-Chlorophenol has been tested on a range of Australian algal species. LC50 and NOEC figures (respectively), both 72-h growth, were as follows.

Freshwater Chlorella protothecoides, 39-45 mg/L and 12.9 mg/L.

Freshwater Selenastrum capricornutum, 51 mg/L and 25.7 mg/L.

Marine Dunaliella tertiolecta, 51 mg/L and 10.3 mg/L.

Marine Nitzschia closterium, 7.7-8.1 mg/L and 1.3 mg/L.

Analogous growth figures were reported for 2,4-DCP.

S. capricornutum 96-h EC50, 102-112 mg/L.

N. closterium, 72-h EC50 of 8.8-9.1 mg/L and NOEC of 0.82 mg/L.

Growth figures (72-h EC50) for N. closterium for 2,4,6-TCP of 4.9-10.1 mg/L.

Johnston et al. (1990) compared the toxicity of PCP to Australian species with the toxicity to introduced species under the same laboratory conditions. For fish the 96-h LC50 under flow through conditions for the native eastern rainbowfish Melanotaenia duboulayi of 1.5 ±0.3 mg/L was similar to the introduced mosquitofish Gambusia holbrooki (1.06 ±0.30 mg/L), and only slightly more than the OECD test species zebrafish Brachydanio rerio (0.95 ±0.06 mg/L). Fogels and Sprague (1977) also reported a 96-h LC50 (flow through) of 1.23 mg/L for B. rerio, which acts as a benchmark for the Australian studies. M. duboulayi was towards the less sensitive end of the range for 29 overseas species. The 48-h LC50 of PCP to O. mykiss (NZ data) varied from 90 µg/L to 1945 µg/L, depending on conditions.

A similar comparison (Johnston et al. 1990) of the toxicities of PCP to six Australian cladoceran species with toxicities to two overseas cladocerans under similar test conditions also revealed that the sensitivity of the Australian species was similar to the overseas ones. C. cornuta was the most sensitive, with 48-h EC50 of 70 µg/L. The 48-h EC50 for C. dubia was 150-300 µg/L and 14-d NOEC (reproduction) was 100 µg/L. Simocephalus vetulus and D. magna has the lowest 14-d NOEC of 50 µg/L. Hickey and Vickers (1992) determined a 96-h LC50 of PCP to the New Zealand mayfly Delatidium sp. of 219 µg/L, similar to their 48-h EC50 for D. magna (187 µg/

L).

The 96-h EC50 (growth) of the alga Pseudokirchnierella subcapitatum was 580-890 µg/L of PCP.

Factors that modify toxicity of chlorophenols

Most of the relevant data are on PCP but some extrapolations can be made. Data on phenol also give an indication of the variations in toxicity with different water conditions. The most significant factors that modify toxicity of PCP (and all phenols) are pH, hardness and temperature. PCP is more toxic at lower pH to algae, most invertebrates and fish (Johnston et al. 1990).

At lower pH, PCP is not fully ionised and is therefore highly lipophilic and more able to penetrate. USEPA (1987d) relates their guideline values according to pH using algorithms for 1-hour and 4-day criteria as follows:

4 days: exp [1.005(pH-5.290]

1 hour: exp [1.005(pH)-4.830]

For example at pH = 6.5, 7.8 and 9.0, the maximum 4-day average concentrations of pentachlorophenol are 3.5, 13.0 and 43.0 µg/L respectively.

Water hardness may affect PCP toxicity but there are few data to support this. Smith et al. (1987) reported a 5-fold difference in EC50s for an alga between hard and soft water. Johnston et al. (1990) found some effect of salinity on toxicity: the 96-h LC50 of PCP at 25°C to the rainbowfish M. duboulayi decreased from 1.5 mg/L at low salinity (30 mg/L NaCl) to 0.28 mg/L at 5000 mg/L NaCI. There was no perceptible difference in toxicity to the cladoceran Ceriodaphnia dubia at salinities between 30 and 2000 mg/L (Johnston et al. 1990).

Temperature did not cause an appreciable effect on the toxicity of PCP to the cladoceran C. dubia between 15 and 30°C. It was 2–3 times more toxic to the rainbowfish M.duboulayi at 15°C and 35°C than at 25°C (Johnston et al. 1990).

Guideline

Reliable freshwater figures could be calculated for six chlorophenols.

Although a high reliability freshwater trigger value (24 µg/L) could be calculated for PCP based on 11 data points, neither the 95% nor the 99% (15 µg/L) protection levels provided an adequate margin of safety for acute toxicity to fish. Hence moderate reliability figures were calculated from 84 acute data points.

Table 8.3.21 Toxicity data from short-term tests considered for guideline derivation for mono-chlorophenols (CP) and di-chlorophenols (DCP) (48h-96 h LC50 or EC50 in µg/L). Trigger values are also reported (µg/L) for slightly to moderately disturbed ecosystems.

Name and CAS no.	2CP (95-57-8)	3CP (108-43-0)	4CP (106-48-9)	2,3-DCP (576-24-9)	2,4-DCP (120-83-2)	2,5-DCP (583-78-8)	2,6-DCP (87-65-0)	3,4-DCP (95-77-2)	3,5-DCP (591-35-5)
Freshwater
Fish	8100-21,000 (n=1)	4500 (n=1)	1900-9000 (n=5)	4000 (n=1)	2000-8300 (n=4)	3300 (n=1)	6400 (n=1)	1900 (n=1)	2300 (n=1)
Crustacean	2600-7430 (n=2)	–	2500-9000 (n=3)	3100 (n=1)	1400-2610 (n=2)	–	3400 (n=1)	–	–
Algae/ciliate	50,000-170,000 (n=4)	29,000 (n=1)	8000-51,400 (n=4)	5000 (n=1)	9200-112,000 (n=4)	12,150 (n=1)	9700-29,000 (n=2)	3200 (n=1)	890-5000 (n=2)
TV Fresh (mod reliab.)	340 (mod; SD; 99%)	–	220 (mod; SD; 95%)	–	120 (mod; SD; 99%)	–	–	–	–
TV Fresh (low reliab.)	–	4.5 (AF)	–	31 (AF)	–	3 (AF)	34 (AF)	2 (AF)	4 (AF)
Tainting threshold x 0.5 (CCREM 1987)	30	na	22	42	0.2	12	18	na	na
Marine
Fish	6300-6600 (n=2)	4000 (n=1)	5000-5400 (n=2)	4380 (n=1)	5130-6830 (n=2)	3290 (n=1)	5400 (n=1)	2300 (n=1)	3500 (n=1)
Algae or ciliate	–	–	10,300-51,400 (n=2)	–	9000 (n=1)	–	–	–	–
TV Marine (low reliab.)	340 (f)	4 (AF)	220 (f)	31 (f)	120 (f)	3 (AF)	34 (f)	2 (AF)	4 (AF)

Table 8.3.22 Toxicity data from short-term tests considered for guideline derivation for tri– (TCP), tetra-chlorophenols (TeCP) and pentachlorophenol (PCP) (48-96 h LC50 and EC50, µg/L). Trigger values are also reported (µg/L) for slightly to moderately disturbed ecosystems.

Name and CAS no.	2,3,4-TCP (15950-66-0)	2,3,5-TCP (933-78-8)	2,3,6-TCP (933-75-5)	2,4,5-TCP (95-95-4)	2,4,6-TCP (88-06-2)	2,3,4,5-TeCP (4901-51-3)	2,3,4,6-TeCP (58-90-2)	2,3,5,6-TeCP (935-95-5)	PCP (87-86-5)
Freshwater
Fish	1100 (n=1)	–	–	450-3060 (n=4)	180-9700 (n=6)	205-450 (n=2)	140-1270 (n=4)	170-3600 (n=2)	18-30001 (n=27)
Crustacean	–	–	–	900-2700 (n=1)	270-6000 (n=1)	–	90-2660 (n=5)	570-2500 (n=1)	70-4320 (n=21)
Other invertebrate	–	–	–	–	5500 (n=1)	–	–	–	110-34000 (n=30)
Algae or ciliate	2000 (n=1)	–	–	–	3500-10000 (n=4)	–	650-10,100 (n=4)	1400 (n=1)	80-10300 (n=7)
TV Fresh (high-mod reliab.; 99%)	–	–	–	–	3 (mod; SD)	–	10 (Mod; SD)	–	3.6 (high; SD)
TV Fresh (lowreliab.)	1(AF)	2 (m)	2 (m)	0.5 (AF)	–	0.2 (AF)	–	0.2 (AF)	–
Marine
Fish	4310 (n=1)	2310 (n=1)	2130-5670 (n=1)	4010 (n=2)	1400-2800 (n=2)	1500-2250 (n=1)	–	1390-2000 (n=2)	90-1700 (n=6)
Crustacean	–	–	–	–	5600 (n=1)	–	–	21,900 (n=1)	70-100003 (n=10)
Other invertebrate	–	–	–	–	–	–	–	–	67-180004 (n=11)
Algae	–	–	–	–	–	–	–	440 (n=1)	3000-5500 (n=3)
TV Marine (mod reliab.; 99%)	–	–	–	–	–	–	–	–	11 (mod; SD)
TV Marine (low reliab.)	4 (AF)	2 (AF)	2 (AF)	4 (AF)	3 (f)	2 (AF)	10 (f)	1.4 (AF)	–

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