Pesticide use and freshwater ecotoxic impacts in biofuel feedstock production: a comparison between maize, rapeseed, Salix, soybean, sugarcane and wheat

Background. Biofuel production is expected to increase significantly over the coming decades. Given that climate change mitigation is a major rationale for biofuel promotion, greenhouse gas savings have so far been a main concern, but there is a need to consider other environmental impact categories as well; for example ecotoxicity due to pesticide use in biofuel feedstock production. Ecotoxicity is an impact category that has often been omitted from agricultural Life Cycle Assessments in the past due to high complexity and lack of consensus regarding characterisation. Aim and scope. The aim of this thesis is to evaluate the environmental performance of a selection of biofuel feedstocks in terms of pesticide use in cultivation and associated freshwater ecotoxic impacts. The feedstocks included are: maize (USA: two cases – with and without insecticide), rapeseed (Europe), Salix (Sweden), soybean (Brazil: GM and non-GM), sugarcane (Brazil) and wheat (Europe). Method. Pesticide use was investigated and typical field application scenarios were constructed. PestLCI 2.0 was used as an emission inventory model to determine emissions to air and surface water and USEtox 1.01 was used as a characterisation model to determine the potential freshwater ecotoxic impacts expressed in Comparative Toxic Units ecotoxicity (CTUe). Additional pesticides, soil and climate profiles were added to PestLCI and additional characterisation factors (CFs) were calculated in USEtox. Pesticide use and ecotoxic impact scores were allocated to biofuels and associated co-products through partitioning based on energy content (no co-products were assumed for Salix and sugarcane). Results. Sugarcane, conventional soybean and maize all require almost the same amount (18−19 g) of pesticide active substance (AS) for production of 1 GJ biofuel energy while rapeseed and wheat require 40% and 80% more respectively. Salix has by far the lowest pesticide AS application rate, both per hectare and year and per energy unit of biofuel output. Concerning freshwater ecotoxic impacts per hectare and year, Salix and rapeseed have the lowest scores (1 and 2 CTUe/ha/yr respectively) and sugarcane the highest: 89 CTUe/ha/yr - which is more than three times that of any other feedstock. The high score of sugarcane is associated with the use of the herbicides atrazine, 2,4-D and ametryn. In relation to biofuel energy output, the impact score of sugarcane is improved in relation to the other crops, due to high energy output. Production of 1 TJ biofuel energy from rapeseed causes an ecotoxic impact score of 31 CTUe, while production of 1 TJ biofuel energy from wheat, maize (insecticide case), GM soybean and sugarcane give rise to ecotoxic impact scores 4, 10, 13 and 22 times larger, respectively. The European cases have lower ecotoxicity scores in general compared to the North and South American cases; probably an effect of stricter pesticide legislation in Europe. The top-three AS with highest ecotoxic impact scores are atrazine (sugarcane, 56.8 CTUe/ha/yr), 2,4-D (sugarcane, 17.8 CTUe/ha/yr) and chlorpyrifos (maize, 16.1 CTUe/ha/yr) – all three of which are known to be problematic pesticides. Conclusions. There is a large variation in freshwater ecotoxic impacts of the assessed alternatives, both when compared to hectare and year and biofuel energy output. In addition, allocation influence the results significantly. There is no correlation between amount of pesticides used and ecotoxic impact caused, but location and timing are highly significant for emissions to various environmental compartments and hence ecotoxic impact scores. The largest challenges were encountered in relation to the dynamic character of pesticide use and in dealing with ecotoxicological effect data in calculation of new CFs. The models used are still immature and further research is needed to develop and make models fully compatible. Due to the limitations of the study, especially in relation to inventory of pesticide use, the ecotoxic impacts cannot be interpreted as fully representative for the crops in general. However, Salix has the lowest (most favourable) score in all environmental performance indicators and it is likely that a future biofuel from Salix would be associated with lower pesticide use and associated freshwater ecotoxic impacts compared to the other alternatives