Appendix D - Dossier (PDF) - Tera

date: 20–JUL–2005
4. Ecotoxicity Substance ID: 71–43–2
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4.4 Toxicity to Microorganisms e.g. Bacteria
Type: other: Microbial toxicity in soil medium
Species: other bacteria: Polytox commercial microbial test culture
Exposure period: 10 hour(s)
Year: 1998
GLP: no
Remark: A laboratory procedure using automated respirometry was
developed to measure microbial toxicity in soils as a
function of respiration inhibition. Sterilized sandy loam
soil; source: agric field, N.M USA, organic content 0.7%,
autoclaved 7hr/4d, 200g/test system; remoisturized w/ dH2O
to 33, 50, 80 and 100% moisture to determine % moisture
effects on toxicity. Microbes: Polytox, commercial
freeze–dried product – blend of 12 strains of aerobic
microbes– supp Polybac Corp. Bethlehem, PA. EPA recommended
microbial culture for effluent tox testing(doc 440/4–87–005,
7/1987).Cells resuspended in nutrient buffer, and 1:10
dilution of resuspended cell volume to soil mass used for
testing. Cell density of inoculum not reported. Acetone
was used as a cosolvent for chemical addition.
Concentration verification of spiked soils by GC/MS
indicated homogenous soil concentrations. During a 10 hr
test duration, respiration was monitored. IC50 calculated
based on reduction of oxygen uptake rate in chemical test
systems versus control reator. The test protocol was
reproducible with a mean standard deviation of 0.08 mg
chemical/g of soil for eight chemicals.
Effect of acetone (as cosolvent) is unclear, since solvent
blank (0.5 ml acetone/200 g soil) preparation is described
as a control system. Determination of IC50 is calculated by
comparison of respiration rates of chemicals to control; it
is not clear if the control contains only soil, or acetone
in soil. IC50 values for acetone are also reported, which
infers soil blanks where used as comparison. It is also
unclear whether the acetone concentration used as co–solvent
affected respiration. Toxicity is not significantly
affected by % mositure for these chemicals.
Result: Benzene IC50 Values at Different Soil Moisture–Holding
Capacities (mg chemical/g soil)
Moisture –holding capacity
33% 50% 80% 100%
IC50 0.51 0.51 0.48 0.30 0.75 0.71
n1 4 6 6 7 4 4
r2 0.990 0.916 0.985 0.690 0.844 0.965
Correlation between toxicity tests done in aqueous medium
and soil for Polytox test culture was statistically
significant and yielded an r2 of 0.816.
In comparison, benzene was determined to have an IC50 value
of
679 mg/l for the Polytox culture in aqueous medium.
Source: Exxon Biomedical Scineces, East Millstone, NJ, USA
Appendix D: Benzene SIDS Dossier
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