Elemental sulfur occurs naturally in marine and limnic sediments. Elem
ental sulfur, brought in solution in aqueous media by using organic so
lvents such as methanol as carrier solvent, was toxic in a bacterial l
uminescence test, known as the Microtox test. Previously, it has been
shown that the toxicity in the luminescence test of whole sediments al
so was correlated to i.a. elemental sulfur using multivariate statisti
cal analysis. Organic solvent extracts of sediments obtained in receiv
ing waters of effluents from a pulp and paper mill was toxic in the lu
minescence test, and using a toxicity evaluation procedure, the toxic
substance was identified as octameric cyclic sulfur, S-8. The substanc
e dominated the toxicity in extracts of both a contaminated sediment a
nd a sediment from a control area. Since the toxicity in the Microtox
test of aqueous solutions of S-8 decreased upon storage, a conversion
process of the toxic form was indicated. Acute toxicity of S-8 was not
limited to the luminescent bacteria in the Microtox test, but was obs
erved in tests with fish larvae if tested with the transient form of e
lemental sulfur. Tests of acute toxicity with zebra fish and perch lar
vae were responsive to elemental sulfur. Probably, the toxic form of e
lemental sulfur is the single cyclic octamer, that due to low aqueous
solubility, binding to particulate sediment material or aggregation is
converted into a nontoxic form. Acute toxic effects may occur in sulf
ur containing sediments of varying,redox potentials or where elemental
sulfur deposits are turbated. (C) 1998 by John Wiley & Sons, Inc. Env
iron Toxicol Water Qual 13: 217-224,1998.