Mass loss measurements confirmed the photographic evidence that the CDA and positive control materials disintegrated in seawater within months ( Figure 2). Isotopic mass balance equations were used to determine the amount and source of C respired to CO 2 by the native microbial communities during the incubation ( Section S14). At the end of the experiment, all samples were submitted to NOSAMS for DI 13C and DI 14C analysis. At set time points (0, 2, 4, and 6 days for the CDA treatment and 0 and 6 days for the control treatments), the incubation was ceased with a spike of a saturated HgCl 2 solution.
Incubations took place in the dark at 20 ☌ on a shaker table set at 15 rpm. After 10 weeks in the continuous flow mesocosm, the test materials were transferred to 125 mL respirometry bottles and filled with 100 mL of nutrient-amended seawater to exclude the possibility of oxygen and nutrient limitation during the 6-day incubation. There were four experimental treatments: (i) seawater only, (ii) CDA and seawater, (iii) cellulose (positive control material) and seawater, and (iv) LDPE (negative control material) and seawater. Lastly, shifts in the Δ 14C and δ 13C of the dissolved inorganic carbon (DI 14C and DI 13C, respectively) during short-term bottle incubations assessed if native marine microbes respire CDA and control materials to carbon dioxide. Our collective findings demonstrate that CDA-based materials disintegrate and biodegrade in the ocean orders of magnitude faster (months) than previously reported (decades). Enzymatic assaying and analysis of the natural abundance radiocarbon ( 14C) and stable carbon ( 13C) isotopic composition of the carbon dioxide (CO 2) respired during short-term bottle incubations documented biodegradation of these materials. Time-lapse photography and mass loss measurements documented the disintegration of these materials. As negative controls, (10−12) we tracked a polyethylene (LDPE) film and polyethylene terephthalate (PETE) fabric.
As positive controls, (9) we tracked Kraft paper film and cotton fabric, both cellulosic in nature. Four formulations of CDA were tracked over time in the mesocosm, including nonplasticized and plasticized (triacetin) CDA 25 μm films, a plasticized (triacetin) 510 μm CDA foam, and a nonplasticized CDA fabric (97 g/m 2). Here, we incubated CDA-based materials and positive (high degradative capacity) and negative (low degradative capacity) control materials in a mesocosm equipped with a continuous flow of coastal seawater (Vineyard Sound, Massachusetts, United States see the Supporting Information for experimental details). These findings challenge the paradigm set by governmental agencies and advocacy groups that CDA-based materials persist in the ocean for decades, and represent a positive step toward identifying high-utility, biobased plastics with low environmental persistence. The natural abundance stable ( 13C) and radiocarbon ( 14C) isotopic signature of carbon dioxide respired during short-term bottle incubations confirms the rapid degradation of both acetyl and cellulosic components of CDA by seawater microbial communities. Disintegration is marked by the increasing esterase and cellulase activity of the biofilm community, suggesting that marine microbes degrade CDA. Photographic evidence and mass loss measurements demonstrate that CDA-based materials disintegrate in months. Here, we probe the disintegration and degradation of CDA-based materials (25 μm films, 510 μm foam, and 97 g/m 2 fabric) by marine microbes in a continuous flow seawater mesocosm. The persistence of cellulose diacetate (CDA), a biobased plastic used in textiles and single-use consumer products, in the ocean is currently unknown.