Life Cycle Assessment of Seaweed-Based Biostimulant Production: Environmental Hotspots, Cultivation Pathways, and Nutrient Substitution Potential

Abstract

Seaweed-based biostimulants have emerged as promising sustainable agricultural inputs due to their potential to enhance crop productivity, improve nutrient use efficiency, and increase tolerance to abiotic stresses, thereby reducing dependence on synthetic fertilizers. However, the environmental performance of their production systems remains insufficiently quantified. This study presents a cradle-to-gate life cycle assessment (LCA) of a formulated seaweed-based biostimulant derived from Kappaphycus alvarezii, based on representation of a real-world industrial-scale production system in India. Environmental impacts were evaluated across cultivation, biomass transport, sap extraction, and packaging stages using the ReCiPe 2016 midpoint method, with a functional unit of 1 L of packaged commercial seaweed biostimulant at the factory gate. Results indicate that the baseline raft-cultivation system, climate change impact was 0.123 kg CO2-eq per L of packaged commercial biostimulant. Packaging accounts for approximately 74% of cradle-to-gate climate change impacts, primarily due to plastic material production, while extraction contributes ∼21%, largely driven by electricity consumption (>92% within the stage). In contrast, cultivation contributes less than 5% of total cradle-to-gate impacts, with wild harvest having higher impact across most categories compared to raft-based methods. Within raft-based cultivation, polypropylene ropes (53.4%) and HDPE nets (34.6%) account for nearly 88% of impacts, whereas diesel use dominates wild harvesting (∼86.4%). Also, sensitivity analysis shows that increasing transport distance from 50 km to 300 km can increase total climate change impacts by ∼45. An additional multimodal transport scenario (road–sea–road), representing potential international biomass sourcing, resulted in higher transport-related impacts but did not alter the identification of packaging and extraction as the dominant environmental hotspots. Packaging sensitivity analysis indicates that replacing 50% of virgin HDPE with recycled material reduces overall climate change impacts by ∼18.40%. An exploratory baseline substitution scenario, based on nutrient-equivalent offsets of potassium and phosphorus using a system expansion approach, indicates that partial substitution of conventional fertilizers can reduce climate change impacts by approximately 17%. This represents a conservative estimate because it excludes additional field-validated biostimulant effects, such as improved nutrient-use efficiency and crop productivity, which may provide further environmental benefits.