Phenol in freshwater and marine water
Toxicant default guideline values for protecting aquatic ecosystems.
Extracted from Section 8.3.7 ‘Detailed descriptions of chemicals’ of the ANZECC & ARMCANZ (2000) guidelines.
The default guideline values (previously known as ‘trigger values’) and associated information in this technical brief should be used in accordance with the detailed guidance provided in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.
Description of chemical
Phenol (CAS 108-95-2), or monohydroxybenzene, is an aromatic organic acid with effective biocidal properties. Its formula is C6H6O. It has a low log Kow and is soluble in water to 82 g/L at 15°C.
Uses and environmental releases
Phenol (CAS 108-95-2) is a commonly used raw material for manufacture of a range of organic products including phenolic resins, salicylic acid, pentachlorophenol, bisphenol-A (for polycarbonates and epoxy resins), aniline, alkyl phenols and cyclohexanol (for nylon and other fibres). It is also used as a household and industrial disinfectant. World consumption in 1990 was estimated at 4,500,000 tonnes (Crookes & Howe 1996).
Phenol is a common by-product of refining or treatment of fossil fuels, e.g. gas and coke production from coal and crude oil refining. Emissions of phenol from oil refineries in the UK in 1992 were estimated (Crookes & Howe 1996) at between 9 and 1950 tonnes, depending on the type of refinery, for 92 million tonnes of crude oil refined. Around 30 million tonnes is refined in Australia (figures derived from Black et al. 1994). Phenol is a common contaminant of disused gasworks sites. It is estimated that 0.8 to 1.5 kg of phenol is produced per tonne of coke produced (Crookes & Howe 1996). There are many other diffuse sources of phenol, both natural and anthropogenic (Scow et al. 1981).
Phenol is relatively volatile and is readily soluble in water. Most monohydric and dihydric phenols, readily undergo oxidation and microbial degradation, depending on the conditions of the ecosystem (USEPA 1979c). The rate of adsorption of phenol is not clear, as biodegradation tends to dominate in a wide range of water, soil, sediment and biological conditions (Crookes & Howe 1996). Phenol has a low log Kow (1.46) and is unlikely to bioaccumulate, which accords with most of the literature (Crookes & Howe 1996). Depuration of phenol is rapid with half-life ≤ 12 hours. It is not expected to volatilise from water but may do so from land, and be removed from the atmosphere by rain (Kawamura & Kaplan 1983, Leuenberger et al. 1985, 1988). The current analytical practical quantitation limit (PQL) for phenol is 2 µg/L (NSW EPA 2000).
There have been a number of reviews on the toxicology of phenolic compounds (EIFAC 1973, Buikema et al. 1979, USEPA 1979c, Crookes & Howe 1996). LC50 (≥ 48 h) values for phenol varied widely with different phyla and test conditions; from 2 to 2200 mg/L. Phenol does, however, impart tastes and odours to flesh of fish and shellfish at low concentrations and many guideline figures have reflected this propensity.
Acute and chronic toxicity data that supported the derived guideline figures are outlined below (in mg/L, i.e. x 1000 µg/L). There were data for 150 freshwater species and around 25 marine species.
Freshwater fish: 32 species, 48 to 96-hour LC50, 1.6 to 100 mg/L; > 90% of figures were < 50 mg/L.An outlying figure of 1.75 µg/L for Cyprinus carpio was not used because it was 3 to 5 orders of magnitude lower than other figures for the same species. Chronic no observed effect concentration (NOEC) values, for 35 days for growth of Oncorhynchus mykiss were 800 to 2780 µg/L (geometric mean 1680 µg/L) and for 85 days for mortality, were 120 to 3980 µg/L (geometric mean 1090 µg/L), giving an acute-to-chronic ratio (ACR) of 52.
Freshwater amphibians: the toxicity of phenol to embryo-larval stages of eight species of amphibians (LC50, 4 days post-hatch, 9 days total exposure), ranged from 0.04 to 9.9 mg/L (Birge et al. 1980, Black et al. 1982). However, Holcombe et al. (1987) found the South African clawed toad (Xenopus laevis) insensitive (96-hour LC50 > 51 mg/L). These data did not meet the selection criteria. In addition, the low figures failed to meet statistical criteria for demonstration of a significant effect (see Section 188.8.131.52 of the ANZECC & ARMCANZ 2000 guidelines).
Freshwater crustaceans: Acute 48 to 96-h LC50 or EC50, 28 species, 3 to 200 mg/L. Asellus, Gammarus and several copepods were least sensitive. Almost 60% of the figures were < 50 mg/L and around 20% were < 10 mg/L. Chronic NOEC figures are as follows: for the USA Ceriodaphnia dubia (7-day) of 6500 µg/L (reproduction) and 840 µg/L for mortality;and for Daphnia magna, 16 days, growth of 160 µg/L and 9-day mortality and reproduction of 500 to 3900 µg/L. ACRs were around 25 for mortality and around 3 to 10 for reproduction.
Freshwater insects: Acute 48 to 96-hour LC50, 45 species, 2 to 2200 mg/L. Some mayflies were amongst the most sensitive and flower flies and beetles among the least.
Freshwater molluscs: Acute 48 to 96-hour LC50, 23 species, 138 to 1000 mg/L.
Other freshwater invertebrates: Acute 48 to 96-hour LC50, 19 species, 32 to 1280 mg/L.
Freshwater algae: 96-hour EC50, growth, three species, 46 to 370 mg/L.
Marine fish: 48 to 96-hour LC50 for nine species, 5.2 to 44 mg/L.
Marine crustaceans: 48 to 96-hour EC50/LC50 for eight species, 5.8 to 186 mg/L. A mysid shrimp was most sensitive.
Marine molluscs: 48 to 96-hour LC50 for two species of 54 to 565 mg/L.
Marine algae: 72-hour EC50 for two species of 50 to 54 mg/L. 5-day NOEC for biomass and population growth of 13 mg/L.
Model ecosystem studies: Pratt et al. (1989) studied the effect of phenol, at concentrations ranging from 0.3 to 30 mg/L for a period of 21 days, in laboratory ecosystems included bacteria, protozoa, algae, fungi and small metazoa taken from two different field sites. Estimated maximum acceptable toxic concentrations (geometric mean of NOEC and LOEC) for phenol, based on dissolved oxygen production, were 5.7 and 3.0 mg/L for the two sites. This did not meet requirements for replication, treatment or range of taxa, and cannot be used.
Toxicity to Australian and New Zealand species
Johnston et al. (1990) reported that 48-hour EC50s of phenol at 25°C to six Australian cladocerans varied from 7 mg/L for Daphnia carinata to 37 mg/L for Simocephalus vetulus. This compared to 5 mg/L for D. magna and 11 mg/L for the USEPA C. dubia Richard, tested under the same conditions, and were towards the lower end of the range for overseas species. Patra et al. (1996) reported a measured 48-hour EC50 to Australian C. dubia of 19 mg/L at 25°C (awaits peer review).
The measured 96-hour LC50s for rainbowfish, Melanotaenia duboulayi, and golden perch, Macquaria ambigua, were 20 mg/L compared to 23 mg/L for introduced mosquitofish, Gambusia holbrooki, and 10 mg/L for zebrafish, Brachydanio rerio (Johnston et al. 1990). These were all within the range for overseas data.
The 96-hour EC50 for growth inhibition of the Australian green alga, Scenedesmus obliquus, was 102 mg/L (Johnston et al. 1990), while the lowest concentration tested, 31 mg/L, caused a significant effect. The 96-hour EC50 to Selenastrum capricornutum was 46 to 84 mg/L, and to the marine diatom, 50 mg/L. These were within the range of toxicities of overseas species.
Phenol significantly affected reproduction of C. dubia at 25°C between 1.2 and 2.7 mg/L (nominal figures), around 10% of the acute EC50, and for C. cornuta at around 5 mg/L (Johnston et al. 1990). Patra et al. (1996) determined a measured NOEC figure for C. dubia of 0.74 mg/L at 25°C, giving an acute/chronic ratio of 16 (awaits peer review).
Factors that modify toxicity of phenol
The main water quality parameters that modify the toxicity of phenol, and most other phenols, are pH, hardness, temperature and dissolved oxygen. Some contradictory results were obtained and managers are advised to adopt a precautionary approach.
Phenol ionises at higher pH and it could be expected that its toxicity would be higher in the un-ionised form, i.e. at lower pH values, where penetration of biological membranes would be greater (Kaila & Saarikoski 1977). Flerov (1973) and Herbert (1962) found that the toxicity of phenol to fish varied little over intermediate pH values, e.g. 5.8 to 8.1. On the other hand, Dalela et al. (1980) and Verma et al. (1980) have shown that the toxicity of phenol to fish increased with decreasing pH. The toxicity at pH 4.6 to three species of teleosts was between 3 and 5 times greater than at pH 7.3. The factors at pH 6.0 and 8.8 were 1.1 and 0.4 to 0.7 respectively (Dalela et al. 1980). It would be precautionary to use these factors in the site-specific approach.
Literature on the effect of hardness on phenol toxicity is also contradictory. Rainbow trout O. mykiss, carp C. carpio and mosquitofish Gambusia affinis were less sensitive to phenol in hard water than in soft water (EIFAC 1973) and there was no difference for P. promelas (Pickering & Henderson 1966a). Birge et al. (1979b) found that the toxicities of phenol to early life-stages, 4 days post-hatch, of O. mykiss and goldfish Carassius auratus increased as hardness increased by factors of 7 and 3, respectively, from 50 to 200 mg/L CaCO3.
For temperature literature is also conflicting, probably due to competing processes of increased rate of intake of phenol and rate of toxic action versus rate of excretion at higher temperatures. Toxicity of phenol increased at higher temperatures for the fish Carassius auratus (Cairns et al. 1978; 2 fold decrease in LC50 from 5 to 15°C) and Lepomis macrochirus (Ruesink & Smith 1975), and the freshwater invertebrate Philodina acuticornis (Alekseev & Antipin 1976). Cowgill et al. (1985) reported a 3-fold increase in toxicity to the cladoceran C. dubia as temperature increased from 20°C to 24°C and a 1.5 fold increase for D. magna. In contrast, phenol was less toxic at higher temperatures to the freshwater crustacean Asellus aquaticus (Green et al. 1988, McCahon et al. 1990), rainbow trout O. mykiss (Brown et al. 1967a, Cairns et al. 1978), and to various carp species (Jiang & Cao 1985). However, the time to death of trout decreased with increasing temperature. Reynolds et al. (1975) found phenol more inhibitory to growth of the freshwater alga Selenastrum capricornutum at 24°C than at either 20 or 28°C.
In Australian studies with the rainbowfish Melanotaenia duboulayi, Johnston et al. (1990) found a trend of higher toxicity at lower temperature. The LC50 increased from 18 mg/L at 15°C to 23 mg/L at 25°C and 28 mg/L at 35°C. Patra (1999), in experiments designed to test temperature trends, found that phenol was 2 to 3 times more toxic to the rainbowfish at both 15°C and 35°C than at intermediate temperatures. This trend was also apparent in LT50 experiments at different temperatures for two Australian fish and rainbow trout but not for western carp gudgeon Hypseleotris klunzingeri (Patra 1999). For the Australian cladoceran C. dubia, mortality increased significantly with increased temperature (Johnston et al. 1990). Patra et al. (1996) reported that 48-h nominal LC50s decreased from 120 mg/L at 15°C to 15 mg/L at 30°C; measured figures decreased from 48 mg/L at 15°C to 14 mg/L at 30°C. Chronic toxicity to cladocerans also increased with increased temperature. Patra et al. (1996) reported that measured NOECs for reproductive impairment decreased 12.5-fold from 2.5 at 20°C to 0.2 at 30°C. Low oxygen levels generally increase the sensitivity of trout to phenols (Herbert 1962). Aeration decreases the availability, and hence overall toxicity, of phenols by volatilisation (Buikema et al. 1979).
Brown et al. (1967b) found that increasing salinity increased effect on the toxicity of phenol to acclimated rainbow trout: there was a 1.8-fold increase in toxicity from fresh water to 60% seawater. Babich and Stotzky (1985) found that toxicity to filamentous fungi was increased by elevated salinity, comparable with that of estuaries and offshore waters. Johnston et al. (1990) found that increased salinity did not affect the toxicity of phenol to the Australian rainbowfish M. duboulayi at 25°C between 30 mg/L and 5000 mg/L NaCl. However, phenol was significantly more (2 to 2.5 times) toxic to the waterflea C. dubia at 30 and 100 mg NaCl/L (48 h) than at 1000 and 2000 mg NaCl/L.
A freshwater moderate reliability trigger value of 320 µg/L was derived for phenol using the statistical distribution method at 95% protection and an ACR of 16.3.
The anomalous LC50 figure for C. carpio was not used, as the UK reviews recommended against adopting these results (Crookes & Howe 1996). One NOEC figure for D. magna growth was 160 µg/L but other end-points were considerably less sensitive. In view of the large database and the fact that the other cladocerans were less sensitive, the 95% protection level was considered to be sufficiently protective of slightly to moderately disturbed systems.
A marine moderate reliability trigger value of 400 µg/L was derived using the statistical distribution method with 95% protection and an ACR of 16.3.
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