Additionally, several studies were conducted using closed-system bottle incubations, which can lack environmental relevance because the plastic in question is used as the sole nutrient source of carbon. Results of these studies often report much faster degradation rates than those from more realistic mesocosm and field experiments (Table ). Moreover, the few reports of kd pale compared to the vast number of plastic formulations contributing to the large variability across plastic types. For example, in the case of PHAs (Figure ), kd values span nearly two orders of magnitude. Consequently, while PHAs could be materials with the least cost of pollution (Figure ), they could also be some of the more costly choices. In the case of PA, only one study has measured kd (Table ), making any estimate of PA lifetime and cost of pollution highly uncertain. Such tremendous variability and uncertainty pose significant challenges to material selection.