Including pathogen risk in life cycle assessment: the effect of modelling choices in the context of sewage sludge management

Artikel i vetenskaplig tidskrift, 2016

Purpose: Recent attempts to include adverse effects of pathogens on human health in life cycle assessment (LCA) have focused on integrating results obtained through quantitative microbial risk assessment (QMRA) as an impact category in LCA. This study aimed to investigate whether the use of QMRA can be an adequate way of integrating pathogen impact potential in LCA and to quantify how pathogen impact potential is affected by choices regarding model structure and mathematical relationships used. Methods: This study was performed for the context of sewage sludge management and is based on pathogen concentrations in treated sludge reported in the literature. Eight reference pathogens were included in order to address important microbial groups. The pathogen impact potential associated with land application of sewage sludge was quantified based on a QMRA model for eight distinct exposure pathways. The modelling choices investigated were linearisation of dose-response and severity assessment and different modelling approaches and parameter choices in fate and exposure assessment. Results and discussion: The linearisation of effect and severity assessment had a minor impact on the results for exposure pathways where pathogen doses were low but had a major impact where pathogen doses were high. The assumptions regarding fate and exposure conditions, such as pathogen decay time, number of individuals exposed and frequency of exposure, had a significant effect on overall pathogen impact potential. If pathogen impact potential is to be integrated in LCA, a range of different parameterisations for each exposure event may be warranted rather than only the one with the highest risk per individual exposed as commonly reported for QMRAs. This is also in line with the ordinary LCA practice of focusing on average rather than extreme conditions. Conclusions: This study suggests that the use of QMRA can be an adequate way of integrating adverse effects of pathogens on human health in LCA. However, analysts should be careful when choosing model parameters such as the number of people exposed or the frequency of exposure, as LCA may require a different parameterisation than an ordinary risk assessment (RA). Therefore, a direct integration of the results of a QMRA study into LCA may be problematic. Also, in order to avoid potential bias, analysts should carefully consider whether or not pathogen impact potential and human toxicity potential need to be estimated based on a similar set of exposure pathways.