Comments on "Dredging in an estuary causes contamination by fluid mud on a tourist ocean beach. Evidence via REE ratios" by N. Mirlean, L. Calliari, and K. Johannesson in Marine Pollution Bulletin 159 (2020) 111495. https://doi.org/10.1016/j.marpolbul.2020.111495.

N. Mirlean, L. Calliari, and K. Johannesson examined the REE paired La/Eu and Gd/Yb ratios in the region of Patos Lagoon estuary/Brazil and related coastal waters. They concluded that "the mud deposition events at the beach were most likely associated with dredging processes in the estuary especially where overflow is the source of fluid mud on the beach shoreface". In this response to that study, we reflect on several discrepancies in their methods, results and conclusions. In this work, we demonstrate that the approach adopted by the authors does not provide evidence that the selected REE ratios measured on muddy deposits on the beach were derived from dredged activities, particularly regarding overflow. On the contrary, based on their results, the REE ratios presented in the suspended sediments collected in the navigation channel are most likely associated to natural sediments.

Antifouling paint particles: Sources, occurrence, composition and dynamics.

Sources, occurrence, composition and dynamics of antifouling paint particles (APPs) were assessed in Patos Lagoon estuary (PLE), Southern Brazil. Ten areas including boatyards, a marina and artisanal fishing harbors were identified in the estuarine system as potential sources of APPs. The APPs generated in these areas were highly heterogeneous considering the size, shape and composition. Based on an estimate of antifouling paint usage and amount of boats in each studied area, artisanal fishing harbors could be the main source of particles to PLE. However, relatively high amounts of APPs, which ranged from 130 to 40,300 µg g-1, were detected in sediments collected in front of boatyards and a marina. The uneven distribution of APPs levels among the sediment samples were probably due to the presence of diffuse sources (fishing harbors) associated to "hotspots" (boatyards and marina) along the study area. Additionally, data of settling experiment indicate that size, shape and density of APPs, combined to local hydrodynamics, appears to contribute to the mobility of these residues within the estuary. In the main channel of PLE, smaller particles tend to be transported to adjacent coastal zone while particles tend to be deposited in the sediment surface of sheltered areas. Since different trace metals, and booster biocides were detected in APPs that were not correctly disposed, these particles can be considered as an important source of contamination to aquatic environments. The present data suggest that APPs represent an environmental problem for aquatic systems in Brazil, since the country lacks legislation in addition to inefficient control mechanisms. An improvement in boat maintenance processes are urgently needed to avoid this continuous release of APPs into the aquatic systems.