This is the second part of a three-part series explaining the technicalities of product toxicity labelling. This instalment will explain how to interpret product Safety Data Sheets (SDSs) and product warning labels.

Chemicals can be identified via a number of different pathways. The chemical databases referred to in part one and SDSs will typically include either CAS or UN numbers or both. A Chemical Abstract Service Number (CAS Number) is a numerical designation assigned to a single chemical. Mixtures can also be assigned a CAS Number.

UN Numbers relate to ‘Dangerous Goods’ classification and are predominantly intended for transport information. The UN number is a four-digit catalogue number developed by the UN. They can be assigned to a single substance or to a group with similar characteristics or hazardous properties.

CAS and UN numbers identify the chemical, but to describe the potential impacts of chemicals a variety of indicators such as Risk Phrases (R-Phrases) and Safety Phrases (S-Phrases) or more recently Hazard Statements (H-Statements) and ‘Toxicity Indicators’ are used.

R-Phrases give a general indication of the potential effect of a chemical. They can be represented by either a number or a phrase (e.g. ‘R39 Danger of very serious irreversible effects.’) They can be listed as single numbers to denote separate statements or with an oblique (/) linking more than one number that denotes a combined statement of the phrases involved in the impacts of a specific substance.

H-Statements are replacing R-Phrases under the newest of the EU’s REACH and UN Globally Harmonized System of Classification and Labelling of Chemicals (GHS) legislation and are similar in format (e.g. H400: Very toxic to aquatic life). However the H-Statements do not include several key risks that countries like NZ have added to their Hazardous Substances and New Organisms Act to ensure soil toxicity and vertebrate and invertebrate life like bees are included in hazard assessments. This is something Australia will need to consider as we move toward mandatory use of GHS and H-Statements by 2017 with transitional arrangements already in play.

S-Phrases are indicators of precautions that should be taken when handling a product or its container (e.g. ‘S18 Handle and open container with care.’)

There are also a variety of GHS abbreviations and symbols used to classify the toxicity impacts of products as follows:

C       CorrosiveE       ExplosiveF       FlammableF+         Extremely Flammable

N       Dangerous for the Environment


O         OxidisingT          ToxicT+            Very ToxicXi         Irritant

Xn        Harmful


As mentioned in part 1 of this series, toxicity hazard potential is a function of both dose and exposure (Hazard = Dose x Exposure). The dose measures used are NOAEL and NOAC and they are defined as follows:

NOAELs: ‘No Observed Adverse Effect Levels’ are the highest doses that don’t cause ill-effects. A NOAEL refers to a dose of chemical that is ingested.

NOAECs: ‘No Observed Adverse Effects Concentration’ is the highest level of a chemical in a toxicity test that did not cause harmful effects to a plant or animal. A NOAEC refers to direct exposure (e.g. through the skin or gills).

While NOAELs and NOAECs are similar, they are not interchangeable. NOAECs and NOAELs are based on tests that determine the lethal concentration or lethal dose (LC or LD) to a given indicator plant or animal, under test conditions, that impact a given percentage of the population. For example, LC50 and LD50 refer to the lethal concentration or dose that kills 50 per cent of a population under test conditions.

The LD50 is generally expressed as the dose in milligrams (mg) of chemical per kilogram (kg) of body weight. LC50 is usually expressed as mg of chemical per volume (e.g. litre or L) of medium (i.e. air or water) which the organism is exposed to. Chemicals are considered highly toxic when the LD50/LC50 is small and practically non-toxic when the value is large. However, the LD50/LC50 does not reflect any effects from long-term exposure (i.e. cancer, birth defects or reproductive toxicity) that may occur at levels below those that cause death.

NOAEL/NOAEC levels or LC/LD toxicity data are not usually, in themselves, able to assess the toxicity risk levels of products in manufacture, use (except for VOCs or similar cases) or disposal without measures or systems for exposure and/or the likelihood or risk of a critical exposure. To assess the exposure thresholds, other measures are used.

Measures used in OH&S contexts include ‘TWA’, or ‘time-weighted average’ concentration for a normal 8-hour workday or 40-hour work week and STEL’ (ppm or mg/m3) or ‘Short Term Exposure Limit’, the maximum concentration of a substance permitted (a) for a continuous 15-minute exposure period, (b) for maximum of 4 such periods per day, (c) with at least one 60-minute exposure-free period between two exposure periods, and (d) provided the daily TWA is met.


Next month’s instalment will deal with human health impact categories and indicators.