Is natural always greener? Evaluating the environmental performance of lab-scale biopolymer adsorbents

Bio-based materials are widely assumed to provide sustainable alternatives to conventional synthetic technologies. However, whether this assumption holds when evaluated across production and processing pathways remains largely untested. Here, we present a systematic assessment of biopolymer-based adsorbents for water treatment by integrating synthesis analysis with partial life-cycle assessment and a performance-normalized environmental index (EPI). We analyze 49 representative biopolymer systems across six material classes and benchmark them against synthetic counterparts. The functional unit of each adsorbent was determined by their adsorption capacity alongside the number of operating cycles. Our results reveal a fundamental eco-efficiency trade-off: the environmental advantages of biopolymers are frequently offset by energy-intensive processing and the use of auxiliary chemicals, leading to environmental impacts comparable to or exceeding those of synthetic materials. Moreover, their adsorption performance does not consistently surpass conventional alternatives, resulting in limited environmental efficiency when normalized to function across multiple uses. Consequently, both lab-scale synthetic adsorbents (median EPI of 0.00535) and mature commercial benchmarks (EPI ranging from 0.00029 to 0.00084) achieved superior (lower) EPI scores compared to the median efficiencies of widely researched lab-scale biopolymers like cellulose and starch (0.023 and 0.0185 respectively). These findings challenge the prevailing assumption that material origin determines sustainability and demonstrate that process-level considerations could dominate environmental outcomes. We show that material-centric choice is not enough and therefore system-level evaluation is vital. We suggest that research transitioning from laboratory to industrial scale should prioritize environmental efficiency over feedstock origin, for sustainable technologies generally and water treatment applications specifically.