Polymer assessment methodology

Polymers are compounds of high molecular weight derived either by the addition of many smaller molecules, e.g. polyethylene, or by condensing many smaller molecules by eliminating water, alcohol, or other simple substances to produce polymers such as nylon.

When assessing polymers under the IMAP Framework—unlike the NICNAS New Chemicals Program where detailed identity and molecular weight information is provided—NICNAS only has access to the chemical name listed on the Australian Inventory of Chemical Substances (AICS).

In addition, polymers are difficult to model using QSARs. Therefore, in order to assign a hazard band or characterise environmental risk, a number of rule-based approaches have been developed. These are based on the Canadian experience when categorising their Domestic Substances List (DSL).

Human health assessment—allocating a hazard band

In the absence of molecular weight data for the majority of polymers on AICS, it will be assumed that the two criteria of number-average molecular weight (NAMW) (>1000 Daltons) and content of low molecular weight species meet the requirements to identify them as polymers of low concern (PLCs).

To assign a polymer to a particular hazard band, the known hazardous properties of a polymer class or reactive functional group (RFG—e.g. isocyanate) are considered. Where these known hazardous properties match a hazard indicator used to assign a hazard band, e.g. respiratory sensitisation, then the appropriate hazard band is assigned. If more than one RFG is present, the polymer will be placed in the highest relevant hazard band. The following rules are applied

1.  Ethoxylates and propoxylates (AEs)

These are not considered to meet the PLC NAMW criteria listed above because lower molecular weight forms of these polymers are frequently used as surfactants. These polymers (with the exception of nonylphenol ethoxylates) are considered to have the potential to be harmful following repeated exposure, and are accordingly assigned to Hazard band 2.

2.  Nonylphenol ethoxylates (NPEs)

Nonylphenol ethoxylates (NPEs) and close relatives have known concerns as endocrine disrupting chemicals (EDCs). Accordingly, these polymers will be assigned to Hazard band 4.

3.  Potential RFGs

For all other polymers on AICS, potential RFGs are identified, then screened against RFGs considered to be of low concern as described in the PLC criteria.

Polymers with RFGs considered to be of low concern are assigned to Hazard band 0. The degradability criterion within the PLC criteria, which mostly applies to biologically derived polymers, is not considered relevant for human health as it relates primarily to environmental considerations, which are being assessed separately. Therefore degradable polymers with RFGs considered to be of low concern are still assigned to Hazard band 0.

4.    Isocyanates

Polymers with isocyanate RFGs fall under the Hazardous Substances Information System (HSIS) classification for isocyanates as respiratory sensitisers, and are accordingly assigned to Hazard band 3. Should NICNAS identify additional RFGs with skin or respiratory sensitisation effects as components of finished polymers, a similar approach will be used.

5.  Polymers with locally-acting

RFGs (RFGs other than those specified elsewhere) are considered likely to be irritants and accordingly assigned to Hazard band 1. Table 1 summarises the hazard band assignment based on polymer class or reactive functional group.

Table 1: Hazard bands for polymers

RFG = Reactive functional groups; AE = Alcohol ethoxylates and propoxylates; NPE = Nonylphenol ethoxylates

Hazard bands for polymers

Hazard band

Hazard indicators

Polymer description

Hazard band 4

Carcinogenic

Mutagenic

Reproductive/developmental toxicity

Endocrine disruption

Neurotoxicity

Polymers closely related to NPEs

Hazard band 3

Acute toxicity—very toxic/toxic (oral; dermal; inhalation)

High chronic/repeat dose toxicity (oral; dermal; inhalation)

Corrosive (irreversible damage)

Respiratory sensitiser

Polymers with isocyanate RFGs

Hazard band 2

Harmful chronic/repeat dose toxicity (oral; dermal; inhalation)

Skin sensitiser

AEs excluding NPEs

Hazard band 1

Acute toxicity—harmful

Irritant (reversible damage)

Polymers with locally-acting RFGs (RFGs other than those specified elsewhere)

Hazard band 0

All indicators fall outside the criteria listed in Hazard bands 1 to 4

Polymers (not AE) with RFGs considered low concern

Environmental risk characterisation

Under the IMAP Framework, chemicals are assessed within a three-tier system. The depth of assessment at each tier is greater than the preceding tier. Starting at Tier I, a chemical proceeds through as many tiers as required until one of two assessment outcomes is reached:

  • the chemical is found to pose no unreasonable risk to the environment; or
  • risk management measures can be implemented to ensure there are no unreasonable risks to the environment.

The environmental risk assessment of polymers consists of three main steps:

  1. hazard evaluation;
  2. exposure evaluation; and
  3. risk characterisation.

Step 1: Hazard evaluation (Tier I)

Consistent with the approach adopted to assess polymers for human health hazards under the IMAP Framework, it will be assumed that the NAMW and content of low molecular weight species for each polymer meet the criteria for PLCs.

The environmental hazard default assumptions for polymers are that all synthetic polymers are persistent and not bioaccumulative. Based on criteria specified for Australia, this equates to a half-life in water >2 months and a bioconcentration factor (BCF) / bioaccumulation factor (BAF) ≤2000.

To determine toxicity at Tier I, each polymer will be assigned to one of three hazard categories (low, moderate or high) based on the available constituent monomer information. A number of rule-based systems, together with expert judgement, are applied to determine the potential for:

  • constituent monomers to have environmental hazard characteristics;
  • degradation in the environment that can release possibly environmentally hazardous substances; and
  • the polymer to sequester essential nutrients (see Table 2).

Table 2: Environment hazard categories for polymers

Environment hazard categories polymers

Environment hazard category for polymers

Polymer characteristics

Low

Non-ionic in the environment

Unmodified natural polymer (not cationic)

Moderate

Degradable synthetic polymer

Structure is a mixture of natural biodegradable components and synthetic components

Indirectly toxic to algae due to the sequestration of nutrients

High—automatically prioritised for Tier II assessment

Cationic in the environment

Forms degradants in the environment that have persistent, bioaccumulative and toxic (PBT) or very(v) PvB hazard characteristics

Forms degradants in the environment that are toxic to aquatic organisms

Step 2: Exposure evaluation (Tier I)

At Tier I, polymers with a known high-concern use-pattern, e.g. direct application to environmental water bodies, will be categorised based on the available exposure information. These polymers will be prioritised for a more in-depth evaluation at Tier II, using more specific exposure models.

For other polymers, the predicted environmental concentration (PEC) will be calculated using applicable standard exposure scenarios and volume-of-use, derived from available, surrogate or default exposure information (refer to the section on Environmental risk characterisation in the framework document for more information).

Step 3: Risk characterisation

Tier I

The risks for polymers with a low environmental hazard category are assessed at Tier I by calculating the risk quotient (RQ). The RQ is calculated by dividing the PEC derived in the exposure evaluation by a conservative predicted no effect concentration (PNEC) set for low environmental hazard polymers as a group. If the RQ <1, the calculation will be validated by checking that the polymer has all of the low hazard characteristics expected of a polymer assessed at Tier I. If all validation steps are passed, the polymer will be considered of low concern to the environment. Otherwise, for RQ ≥1, or if the polymer does not have all of the low hazard characteristics, the polymer will be prioritised for Tier II assessment.

For polymers with a moderate environmental hazard category, a rule-based determination is made as to whether an RQ can be calculated at Tier I based on a conservative PNEC, or whether more sophisticated models (Tier II) are required to determine the risk.

Tier II

At Tier II, refined risk characterisations for polymers are conducted using more sophisticated models for environmental exposure and hazard evaluations, including options to mitigate exposure and toxicity. Where necessary, the possible environmental hazards and risks from polymer degradants will also be assessed.

Last update 4 March 2019