A scale to classify plastic marine debris into physical degradation stages

Marine debris are a widespread problem that affects every river basin, costal and marine environment ever studied for this pollutant. Its full characterization is paramount in the efforts to identify and abate sources, as well as in the raising filed of risk studies. In addition to variables as material, size, colour and shape, state of degradation is also an important feature to be observed, registered and included in numerical analysis that aim at describing marine debris spatio-temporal patterns of distribution. A scale that attributes three degrees, or states, of degradation (1 recent; 2 intermediate; 3 old) to individual marine debris items was created. It is described here together with the criteria adopted to classify among its categories. The scale allows for the inclusion of a relatively difficult to determine factor into statistical analysis as a categorical variable through recognizable levels of physical abrasion. Although degradation is a continuous process, when surveying plastic marine debris the large amount of items does not allow for detailed individual assessment (through chemical and mechanical tests, for instance), and therefore a quick direct observation method adds value to the work without overloading personnel, being time-consuming or resulting in excessive financial costs. We suggest that, until further studies are conduced, the scale is used to compare marine plastic debris items, mainly within surveys.