Plastics can be found in 90% of marine ecosystems. This problem increases with formation of microplastics, particles with diameter less than 5 mm. In aquatic environments, microplastics degrade by environmental factors, being UV radiation the most relevant among them. Furthermore, degradation can influence the plastic toxicity, releasing chemical additives. Therefore, the objective of this study was to analyse the microplastic toxicological potential in aquatic organisms, considering the polymer type and UV radiation exposing time of the particles (aging)[1] . Microplastics with 2 mm in diameter, derived of available commercial materials, were degraded using UV lamp (400W) in different radiation times (2, 8 and 30 hours), meaning 3 months, 1 and 4 years of environmental UV radiation exposition, respectively, following D6954-04 (ASTM) standard. Expanded polystyrene (EPS), polypropylene (PP) and ethylene–vinyl acetate (EVA) were the polymers used. Thereupon, in erlenmeyers having 100 mL of sterile water with salinity 0 and 35 were added photodegraded/aged and new/virgin particles, in different concentrations (5, 25 and 125 particles) according to literature. These solutions were shaken (30 rpm) for 24 and 168 hours in dark. Acute toxicity tests were performed in planktonic crustaceans Artemia salina and Daphnia magna, representing marine and freshwater systems, respectively. A. salina nauplii were exposed to leachates for 24 hours, being evaluated the lethality and alteration in swimming capacity. About the D. magna newborn with 2- and 26-hours age, were exposed for 48 hours to further immobility evaluation. The bioassays showed no effects in both organisms tested. Although the acute bioassays have not shown significant results, the use of more sensitive endpoints such as behavioural response and biomarkers are suggest.