Regulation and Risk Assessment of 1,4-Dioxane - Environmental Investigation and Remediation - page 278

TABLE 6.4
Abbreviations of Common Toxicity Thresholds for Aquatic Organisms

EC 0 Concentration causing an effect in 0% of the test organisms

EC 50 Median concentration causing an effect in 50% of the test organisms

LC 50 Median concentration lethal to 50% of the test organisms

LC 100 Concentration lethal to 100% of the test organisms

LD 50 Median lethal dose for 50% of the test population

LOEC Lowest observed effect concentration

NOEC No observed effect concentration

LOEL Lowest observed effect level

NOEL No observed effect level

PNEC Predicted no effect concentration

TRV Toxicity reference value

concentrations ranging from hundreds to tens of thousands of milligrams per liter (parts per mil-
lion). 1,4-Dioxane is not bioconcentrated in aquatic organisms, animals, or plants; however, it may
accumulate in plants by transpiration (ATSDR, 2004). The European Chemicals Bureau Predicted
No Effect Concentration for aquatic organisms is set at 2700 mg/L (ECB, 2002). There are a variety
of toxicity thresholds used to describe toxic effects of contaminants measured by different tests,
with some expressed as aqueous or mass concentration and others expressed in terms of the dose per
day as a ratio to the body weight of the organism (toxic threshold given in mg/[kg d]). Table 6.4 lists
the aquatic toxicity thresholds discussed in this chapter.
Toxicity reference values (TRVs) provide a benchmark for the toxicity of a contaminant to all the
ecological receptors in an ecosystem, such as freshwater, marine, or sediment ecosystems. TRVs
have not been developed for soil invertebrates and terrestrial plants as toxicity data are not available
(USEPA, 1999). Table 6.5 summarizes the TRVs derived by USEPA for 1,4-dioxane. Similarly,
predicted no effects concentrations (PNEC) are used in Europe to establish the concentration at
which organisms of an ecological compartment are not affected by a contaminant. Table 6.6 pres-
ents PNEC values for the toxicity of 1,4-dioxane to different indicator species.
1,4-Dioxane toxicity data are available for algae, bacteria and protozoa, aquatic invertebrates,
and i sh, as presented in Tables 6.7 through 6.10 . Aquatic toxicity data tabulated here were obtained
primarily from secondary sources (BUA, 1991; NICNAS, 1998; Verschueren, 2001; ECB, 2002;
ATSDR, 2004). Citations of original studies are provided for the reader's convenience but were not
researched for this topic.

TABLE 6.5
Aquatic TRVs for 1,4-Dioxane

Ecosystem TRV [mg/(kg d)] Indicator Species References

Freshwater 62,100 Daphnia magna (water l ea) Bringmann and Kühn (1982)

Freshwater bed sediment 2176 Calculated from freshwater TRV a USEPA (1999)

Marine-Estuarine surface water 67,000 Menidia beryllina (inland silverside) Dawson and Jennings (1977)

Marine bed sediment 2348 Calculated from marine TRV a USEPA (1999)

Source: U.S. Environmental Protection Agency (USEPA), 1999, Screening level ecological risk assessment protocol. U.S.
Environmental Protection Agency, Ofi ce of Solid Waste.
Notes: Sediment TRVs calculated by using equilibrium partitioning assumptions, an assumed fraction of organic carbon in
sediment of 4%, and a K oc of 0.876 for 1,4-dioxane (USEPA, 1999).
a TRV sed = K oc × f oc × TRV sw .