DfE Environmental Toxicity and Fate

3.9 ENVIRONMENTAL TOXICITY AND FATE

Criteria

If a chemical is an acute aquatic toxicant, then it shall biodegrade rapidly and not be bioaccumulative (see Table 3, lines 1-3). If a component has low aquatic toxicity (Table 3, line 4), then its half-life should be less than 60 days.

Table 11 – Environmental Toxicity and Fate

Data Requirements

Measured data are preferred. In the case where measured data are unavailable, data from estimation models or a suitable analog will be accepted as follows:

Acute aquatic toxicity: ECOSAR and data from a suitable analog(s)[5] for comparison to estimated results are preferred. Data, whether estimated or measured, are required for each of the following groups of organisms: algae, aquatic invertebrates and fish (all fresh water). If only estimated data are available for aquatic toxicity, the use of estimated data may be acceptable in combination with EPA expert review. Data for marine species may be added when available.

Bioaccumulation potential: EPI Suite^TM and data from a suitable analog(s) when available. Results from the BAF and BCF models should be considered. An estimated BAF is preferred to an estimated BCF for compounds where log K_ow > 5.

Persistence (measured as level of biodegradation):

(1) If acute aquatic toxicity ≤ 1ppm: Biodegradability must be measured for the chemical or for a suitable analog. Measured results from simulation tests and estimated data from ready biodegradability predictions, such as in EPI Suite^TM, can support weight-of-evidence.

(2) If acute aquatic toxicity > 1ppm and ≤ 10ppm: Biodegradability must be measured or from a suitable analog. Measured results from simulation tests and estimated data from ready biodegradability predictions, such as in EPI Suite^TM, can support weight-of-evidence.

(3) If acute aquatic toxicity > 10ppm and < 100ppm: Biodegradability must be measured or from a suitable analog. Measured results from simulation tests and estimated data from ready biodegradability predictions, such as in EPI Suite^TM, can support weight-of-evidence.

(4) If acute aquatic toxicity ≥ 100pm: Biodegradability for the chemical or for a suitable analog are preferred. Biodegradability predictions from estimation models, such as EPI Suite^TM, may be acceptable. 

Test Methods, Acute Aquatic Toxicity

A baseline data set is required that includes test data in algae, aquatic invertebrates and fish. Additional aquatic toxicity data in other species or in marine species will also be reviewed if available.

Preferred Test Methods for Fish

– OECD Test Guideline 203: Fish, Acute Toxicity Test [79] and

– OPPTS Harmonized Guideline 850.1075: Fish acute toxicity test, freshwater and marine[80] .

NOTE – EPA prefers the flow through method using a mean measured concentration.

Preferred Test Methods for Aquatic Invertebrates

– OECD Test Guideline 202, Part 1, Daphnia sp., Acute Immobilisation Test [81];

– OPPTS Harmonized Guideline 850.1010: Aquatic invertebrate acute toxicity test, freshwater daphnids[82]; and

– OPPTS Harmonized Guideline 850.1035: Mysid acute toxicity test[83].

NOTE – EPA prefers the flow through method using a mean measured concentration.

A 96-hour Mysid shrimp acute toxicity test can be used in place of a daphnid acute toxicity test when the latter is not available.

Preferred Test Methods for Algae

– OECD Test Guideline 201, Alga, Growth Inhibition Test (and biomass) [84] and

– OPPTS Harmonized Guideline 850.5400: Algal toxicity, Tiers I and II (including growth inhibition and biomass) [85].

Alternative Test Methods, Acute Aquatic Toxicity

The following test methods may be considered, when relevant:

– OPPTS Harmonized Guideline 850.1085: Fish acute toxicity mitigated by humic acid [86];

– OPPTS Harmonized Guideline 850.1025: Oyster acute toxicity test (shell deposition) [87];

– OPPTS Harmonized Guideline 850.1045: Penaeid acute toxicity test [88];

– OPPTS Harmonized Guideline 850.1055: Bivalve acute toxicity test (embryo larval) [89];

– OPPTS Harmonized Guideline 850.4400: Aquatic plant toxicity test using Lemna spp. Tiers I and II [90]; and

Test Methods, Persistence (measured as biodegradation)

Data from experimental methods are generally preferred over estimations of persistence. For the purposes of screening safer chemicals in Table 3, rows 1-3, ready biodegradation tests are preferred. It is noted that simulation tests are likely to better describe the biodegradability of a chemical in specific environmental conditions, and these tests can provide information to evaluate the half-life of a chemical that is aquatically toxic at ≥100 ppm. Simulation tests may also contribute useful information in a weight-of-evidence evaluation for chemicals aquatically toxic < 100 ppm.

Preferred Test Methods for Persistence

– OECD Test Guideline 301: Ready Biodegradability (sections A-F)[91];

– OECD Test Guideline 310: Ready Biodegradability – CO2 in sealed vessels [92]; and

– OPPTS Harmonized Guideline 835.3110: Ready biodegradability[93].

– For chemicals where acute aquatic toxicity ≥100 ppm (i.e., line 4, Table 7), the Ready Biodegradability tests specified above, as well as the Inherent Biodegradability tests detailed in OECD Test Guidelines 302 (A-C) [94-96] may be used to determine whether the half-life of a chemical is likely to be less than 60 days. [insert reference to Aronson 2006].

– Simulation tests may also be used to determine the half-life of a chemical and may be useful in a weight-of-evidence evaluation for chemicals aquatically toxic at < 100ppm.

o OECD Test Guideline 309 (OPPTS Harmonized Guideline 835.3190): Aerobic Mineralization in Surface Water - Simulation Biodegradation Test [97],

o OECD Test Guideline 314: Simulation Tests to Assess the Biodegradability of Chemicals Discharged in Wastewater [98],

o OPPTS Harmonized Guideline 835.3280–Simulation Tests to Assess the Primary and Ultimate Biodegradability of Chemicals Discharged to Wastewater.

o OPPTS Harmonized Guideline 835.3170 - Shake Flask Die-Away Test [99], and

o OPPTS Harmonized Guideline 835.3180 - Sediment/Water Microcosm Biodegradation Test [100].

Other Methods of Degradation

On a case-by-case basis, DfE will consider other routes of degradation in the environment, such as hydrolysis or photolysis, and degradation in other relevant media, for example, soil or sediment. In evaluating such degradation studies, DfE will consider the relevance of that degradation pathway to the chemical in question as well as the significance of the degradation. 

Test Methods, Bioaccumulation

A field-measured BAF (located in the literature) is the most preferred data for indicating bioaccumulation.

Alternative Test Methods for Bioaccumulation

When a field-measured BAF is not available, the following test methods may be used:

– OECD Test Guideline 305: Bioconcentration: Flow-through Fish Test[101];

– OPPTS Harmonized Guideline 850.1710: Oyster BCF[102];

– OPPTS Harmonized Guideline 850.1730: Fish BCF[103];

Modeled data from sources such as EPI Suite^TM [2] are acceptable when data are unavailable.