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EC number: 201-964-7 | CAS number: 90-05-1
Toxicity to fish:
No reliable study is available on gaiacol for fish: two data are from secondary literature (primary data not available) and gave on Perca sp. LC50 48H = 70 -80 mg/l (Little, 1970) and LC50 96H = 44 mg/l (unknown species, Gilron et al., 1999). These data can however be used in a weight of evidence approach together with data obtained on a structural analogue of guaiacol, the paramethoxyphenol (isomer in para position), for which two studies quoted in reliability 2 are available. These studies gave a LC50 96H of 28.5 mg/l on Oncorhynchus mykiss (Hodson et al., 1984) and a LC50 96H = 110 mg/l on Pimephales promelas (Geiger et al., 1985). All these data indicate that gaiacol can be considered as harmful for fish.
Toxicity to invertebrates:
Two studies were quoted in reliability 2 according to Klimisch scale. One reported an EC50 24H on Daphnia magna = 63 mg/l (Palla & Dion, 1983) and the other one an EC50 48H = 25.9 mg/l on the same species (Kopperman et al., 1974).
Regarding these 2 studies, gaiacol is considered as harmful for Daphnia.
Toxicity to algae:
One key study has been selected regarding toxicity to algae (Harlan, 2009): conducted in GLP, following OECD 201).
The growth rate NOEC and EC50values based on cell density were 10 and >100 mg/L,respectively. The % growth inhibition in the treated algal culture as compared to the control ranged from -9.4 to 5.4% at 72H.
No abnormalities were noted.
The other data available were all quoted as invalid because of strong deviation to OECD guidelines (durations too short or too long, temperature too high, not agreed species or endpoint tested...), but all led to EC50 > 100 mg/l.
Based on these studies, gaiacol is not harmful for algae.
Toxicity to micro-organisms:
No key study has been selected regarding the endpoint of toxicity to microorganisms. However, a weight of evidence approach can be applied to assess the toxicity to STP microorganisms. Considering first the studies conducted on a mixed inoculum, the following results have been found :
- on Shk1 (genetically modified Pseudomonas extracted from activated sludge of an industrial WWTP) EC50 (bioluminescence inhibition) - 5 min=583 mg/l (Ren & Frymier, 2002)
- on anaerobic activated sludge (methanogenic activity inhibition): EC50 - 48H = 1166 mg/l (Sierra-Alvarez & Lettinga, 1989) and EC20 -48H = 806.9 mg/l (Shcherbakova et al., 1999).
Guaiacol has also been tested on individual bacterial species, likeTetrahymena thermophila (endpoint: motility): LOEC-20 min = 380 mg/l (Gilron et al., 1999).
Three other studies have been considered of low relevance regarding the assessment of STP microorganisms, they nevertheless led to similar results:
On Saccharomyces cerevisiae (growth rate): EC50 -210 min = 227 mg/l (Koch, 1992).
On Vibrio fischerii (bioluminescence inhibition) EC50-30 min = 92.03 mg/l (Nalecz-Jawecki et al., 2000)
On Escherischia coli (cell growth): EC50 -24H = 600 mg/l (Zaldivar et al., 2000)
All these results led to the conclusion that guaiacol is not harmful for microorganisms and that conclusion can be extrapolated to the STP microorganisms as well.
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