Life cycle assessment addressing health effects of particulate matter of mechanical versus manual sugarcane harvesting in Brazil

Concerns about environmental impacts and health effects associated with particulate matter emissions of sugarcane production in Brazil have been raised, mainly due to pre-harvest burning of straw in manual harvesting. In consequence, mechanical harvesting without burning has been increasingly adopted. Life cycle studies have assessed environmental impacts of sugarcane and sugarcane products. However, incorporating health effects of particulate matter 2.5 (PM_2.5) in a life cycle assessment focusing on evaluating the impacts of increasing use of mechanization has not been conducted. This article compares the life cycle environmental and health impacts (with spatially differentiated characterization factors for PM_2.5) of manual and mechanical harvesting of sugarcane in Brazil, and quantifies the health benefits due to the change of harvesting operations.

An attributional life cycle assessment (LCA) of manual versus mechanical sugarcane harvesting was conducted to evaluate the impacts of 1 t of sugarcane at the distillery. ReCiPe was applied to characterize impacts at mid-point (i.e., climate change, fossil depletion, ozone depletion, terrestrial acidification, freshwater eutrophication, human toxicity, photochemical oxidant formation, and particulate matter formation) and end point (i.e., human health, ecosystems, and resources). Impacts on climate change were compared considering different soil carbon sequestration scenarios. Characterization factors (CFs) of health effects of PM_2.5 for Brazil were calculated differentiating emission sources, population densities, and burdens of disease.

At the mid-point, sugarcane production with manual harvesting has higher impacts on photochemical oxidant formation and particulate matter formation mainly due to pre-harvest burning. Mechanical harvesting system may lead to higher impacts on fossil depletion, ozone depletion, and terrestrial acidification resulting from higher use of fertilizers and diesel. Differences of impacts on climate change between two systems vary depending on the soil carbon sequestration scenario. At the end-point level, manual harvesting has higher impacts on human health but lower impacts on resource use. The health effects of PM_2.5 vary considerably with population density. Changing from manual to mechanical harvesting close to urban areas leads to a 93% reduction of health effects, while for rural only 15% and for remote areas 5%. When considering average population density, the health effects of PM_2.5 of manual harvesting were approximately six times higher than mechanical harvesting. Health effects of PM_2.5 calculated with ReCiPe are much lower and may underestimate the effects of primary PM_2.5 emissions.

The results of this article are an incentive to accelerate the mechanization of sugarcane harvesting in areas with lower mechanization levels (i.e., north-northeast region in Brazil and some rough terrain areas) concerning public health benefits. Meanwhile, manual harvesting with straw burning should only be performed in fields located in rural or remote areas. These results can also contribute to further studies comparing potential benefits of sugarcane culture with alternative crops and guide better decision making at regional development level. Spatially differentiated CFs of PM_2.5 calculated in this article may be applied to future studies regarding health effects in the Brazilian context.