Resumen:
Pesticides and Microplastics (MPs) pose a major threat to ecosystem functionality and to biodiversity
15 in estuarine ecosystem. In this study, we assessed two objectives. 1) The concentration of organophosphate
16 pesticides (OPs) and MPs in water and sediments from the burrows, and tissues of the fiddler crabs Leptuca
17 festae and Minuca ecuadoriensis. Both species from Isla Santay, a Ramsar site in the estuary of the Guayas
18 River, Ecuador. 2) The effects of the exposure experiment to microplastic (MP) and its interaction with
19 malathion (MLT) in the survival of M. ecuadoriensis and MPs bioaccumulation. MPs concentrations in the
burrows were up 660 ± 174.36 items kg-1 wet weight and 26 items L-1
20 in collected sediments and water,
21 respectively. Regarding OPs, water and sediment concentrations were up to 26 times above the United States
22 Environmental Protection Agency (US EPA) thresholds for chronic exposure. The highest abundance of MPs
23 in the tissues was found in the gills. OPs concentrations in tissues were below the detection limits. The results
24 of the exposure experiment showed a higher decrease in the survival in MLT+MP treatment (80%) compared
25 to MLT (20%), MP (0%), and control (8%). The bioaccumulation of MPs was reported in the gills, digestive
26 tract, and hepatopancreas. However, the higher concentration of MPs was reported in the MLT+MP treatment.
27 Because MPs can increase the toxicity of malathion in fiddler crabs, which are chronically exposed to MPs
28 and OPs, they represent suitable bioindicators to monitor Isla Santay and to comprehend the effects of human
29 activities on the coastal environment of Ecuador.
