Life Cycle Inherent Hazard: Green Chemistry Metrics based on Intermediate Flows in a Life Cycle Inventory Network Model

There are several well-known examples in green chemistry where process changes to improve a target synthesis have induced the use of highly toxic chemicals two or more steps upstream. The Principles of Green Chemistry focus... [ view full abstract ]

There are several well-known examples in green chemistry where process changes to improve a target synthesis have induced the use of highly toxic chemicals two or more steps upstream. The Principles of Green Chemistry focus on direct synthesis steps, yet no automated approach has been developed to measure the inherent toxicity of these intermediate chemical inputs.  LCA approaches on the other hand do not consider inherent risk at all and focus solely impacts from chemical releases and subsequent exposures.  Here we present a new modeling algorithm, based in a network representation of chemical LCI datasets, specifically ~200 organic chemicals in the ecoinvent life cycle inventory database.  For each organic chemical we can calculate a new metric of ‘life cycle inherent hazard’, where hazard data are applied representing toxicity, flammability, corrosivity, and other common hazard classifications.  Values for inherent hazard are compared to both existing Green Chemistry and LCA metrics, including the toxicity of the target chemical itself.  Results show that there is very low correlation (R²<0.01) between these sets of values, suggesting that current measures of inherent chemical risk that consider only final product synthesis are missing large upstream effects and so do not provide chemists with adequate design guidance.  The new metrics also provide results that are uncorrelated with ‘conventional’ life cycle toxicity results as derived, for example, from the USEtox model.  Life cycle inherent hazard metrics thus provide new information to analysts in both Green Chemistry and LCA communities that reflects risks associated with potential chemical accidents all the way up the chemical synthesis chain.