P&G scientists use QSPRs and QSARs as the first step in a step-wise or tiered approach to environmental fate assessments. Through the mathematical relationships generated by the computational chemistry tools, exposure information can be estimated prior to any data from laboratory research.
We can understand a lot about how a molecule is going to behave from its structure. For example, small molecules containing from one to four carbon atoms are gases at room temperature (methane CH4, ethane C2H6, propane C3H8, butane C4H10). As more carbons are added, the substance becomes a liquid (hexane, a liquid, has six carbon atoms, C6H14) and finally a solid (octadecane, a solid, C18H38).
If we add one oxygen atom to methane (CH4), the molecule formed is a liquid we know as methanol (CH3OH). As we add chlorine atoms, nitrogen atoms or any other atom, we can predict the effect these additions will have on the molecule's behaviour. This behaviour is not limited to predicting whether the molecule is a solid, liquid or gas, but includes predicting how toxic or biodegradable the compound will be.
The tools and approaches used to generate a QSPR (Quantitative Structure Property Relationships) and a QSAR are similar. Which one the scientist uses depends on whether they are predicting a chemical property like solubility in water or a chemical activity like toxicity to algae or humans. Scientists use this information to predict where a chemical goes in the environment (see Fate pages) or the toxicity of a chemical. Since QSARs and QSPRs are equations that help to predict fate or effect values from chemical structures, they are quick and inexpensive to use.
P&G uses a step-wise or tiered approach to fate and effects work, beginning with screening level tools for an initial assessment. More sophisticated tools are used as needed. These different tiers allow P&G to eliminate compounds that will never make it to market for environmental or human health reasons, and to quickly identify less toxic, more rapidly degradable compounds. Ideally, we would like to eliminate problem compounds before much time and money are spent on research and development. QSARs and QSPRs are tier one tools and allow us to understand basic properties, such as toxicity, environmental fate and biodegradability, before any data are generated in the laboratory. From the toxicity, fate and biodegradation information, we are able to estimate exposure and risk to humans and the environment.