Abstract:
Purpose
Stakeholders across the food product supply chain are increasingly interested in understanding the environmental effects of food production. Mushrooms are a unique food crop, grown in the absence of sunlight and in climate controlled environments. Few life cycle assessment (LCA) studies have been conducted previously on mushrooms and none in the USA. This study assesses the cradle-to-gate life cycle environmental impacts of mushroom production in the USA from cultivation to harvest and preparation for bulk packaging.

Methods
This process-based LCA uses primary data from mushroom producers to define the foreground system. Primary data for operations were collected from compost and mushroom producers in the USA, representing approximately one third of US mushroom production. Secondary data were collected from life cycle inventory databases and other published resources to define background systems and process emissions from the foreground system. The study uses a functional unit of 1 kg mushrooms and applies the Institute of Environmental Sciences (CML) impact analysis method, supplemented with additional impact categories for energy use, freshwater use, and 20 and 100-year global warming potentials (GWPs) with and without carbon-climate feedback.

Results and discussion
Results show that GWP100 impacts range from 2.13 to 2.95 kg CO2e/kg of mushroom product, slightly lower than previous mushroom LCAs conducted for Australian and Spanish production systems. Electricity and fossil fuels were the most impactful inputs, not just for GWP, but most other impact categories as well, followed by compost materials, compost emissions, and transportation. Transport of peat, a key input to the mushroom production substrate, and compost materials contributed to 60 and 36% of the total transportation impacts, respectively. The co-product generated by the system, spent mushroom substrate (SMS), was handled using the displacement method. SMS generated very small credits to the system, less than 1% in every impact category.

Conclusions
Recommendations to improve the commercial mushroom production process include reducing electricity and fossil fuel use through on-site renewable energy generation. This recommendation is primarily relevant to mushroom producers in the Eastern region of the USA, where the electricity grid is the most coal and fossil fuel-intensive. Future work should contextualize the results of this study in the context of nutrition, meal, or diet-level assessments to enable informed food choices.