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EC number: 201-152-2
CAS number: 78-87-5
LC50 fathead minnow
Note: the chlorinated aliphatic hydrocarbons are more toxic to the methanogens by about one order of magnitude respect to aerobic heterotrophs. See also below.
of the chemicals tested act by a nonreactive toxicity mechanism.
Reactive toxicity is caused by specific chemical in teractions such as
reaction with an enzyme or interference with a metabolic pathway. In
contrast, nonreactive toxicity (also called nonspecific toxicity or
narcosis, a sort of baseline toxicity) is a function of the quantity of
toxicant that partitions into the biophase.
the toxicants we considered, those that have been previously identified
as known or suspected reactive toxicants are the al dehydes (Kamlet,
1987), acrylates (Russom et al, 1988), acry lonitrile (Kamlet, 1987),
and compounds with low pKa values (Scherrer and Howard, 1979, and
found that chemicals with nitro functional groups and chlorinated
aliphatic hydrocarbons and chlorinated alcohols showed enhanced toxicity
to the methanogens only. Chemicals from these classes were not included
in comparisons and correlations.
of t-tests conducted to compare the sensitivities of each pair of
bacteria and fish indicate whether the log IC50 values are greater than,
less than, or not significantly different from each other at the 95%
confidence level and the best estimate of the mean difference between
the log IC50 values for the pair of organisms and the 95% confidence
interval for that estimate.
Microtox®, and the fathead minnow all had equal sensitivities and were
about one order of magnitude more sensitive than the equally sensitive
aerobic heterotrophs and methanogens.
made between toxicity data for each pair of bacteria and fish were
involved in successful correlations.
aerobic heterotrophs and methanogen toxicity values, with the exception
of the chlorinated aliphatic hydrocarbons, are of the same magnitude as
each other and well correlated. Excluded compounds are more toxic to the
methanogens by about one order of magnitude. The Microtox® bacteria,
Nitrosomonas, and the fathead minnow are more sensitive than the other
two bacteria by about one order of magnitude and all have similar
sensitivities to one another.
is no significant difference between the sensitivities of the aerobic
heterotrophs and the methanogens for most classes of chemicals tested.
Anaerobic processes have a poor reputation for being more susceptible to
process upsets. Our research in dicates that the cause of these upsets
may not be toxicity to methanogens. Solids retention time and other
operating con ditions may be primary determinants of process stability.
The important caveat to this conclusion is that for chlorinated ali
phatic hydrocarbons and alcohols, the methanogens are more sensitive.
When these compounds are present, aerobic processes will be more
resistant to toxic upsets. The best estimate of the mean difference in
log IC50 values between aerobic heterotrophs and methanogens for the
chlorinated aliphatic hydrocarbons and alcohols is 1.22 +/0.43.
finding that aerobic heterotrophs are significantly less sensitive
(approximately one order of magnitude) than Nitrosomonas supports the
common observation that in aerobic processes combining carbon oxidation
and ammonia conversion, the nitrification process is more susceptible to
upsets than carbon oxidation. This phenomenon is caused or exacerbated
by the lower growth rate of the nitrifiers. Our research indicates that
greater susceptibility to toxicity may also be important in
greater sensitivity of Microtox® bacteria compared to aerobic
heterotrophs also confirms previous observations (Dutka et al, 1983;
King, 1984; and Reteuna et al, 1986). Because Microtox® is more
sensitive, it can be used as a screening measurement of toxicity to the
aerobic heterotrophs. A toxicant concentration that does not inhibit
Microtox® will generally not inhibit the less sensitive aerobic
conclusion, aerobic heterotrophs and methanogens showed the same
sensitivity to nonreactive toxicants, with the exception of the enhanced
toxicity of the chlorinated aliphatic hydrocarbons and chlorinated
alcohols to the methanogens. Nitrosomonas, Microtox®, and the fathead
minnow showed the same sensitivity to toxicants, which was significantly
greater than the sensitivity of the aerobic heterotrophs and methanogens.
activated sludge: 520 mg/L/30 min (OECD 209)
fathead minnow: 130 mg/L/96h
Microtox®: 59 mg/L
Nitrosomonas: 43 mg/L
Methanogens: 180 mg/L
fathead minnow compared to aerobic heterotrophs are more sensitive.
Moreover, the chlorinated aliphatic hydrocarbons are more toxic to the
methanogens by about one order of magnitude respect to aerobic
heterotrophs. Although a IC50 value of 1,2-dichloropropane for aerobic
heterotrophs is not available, it is expected that it would be higher
than the value for methanogens.
IC50 Microtox® of 59 mg/L can be used as a worst case toxicity value.
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