Brazilian Environmental Authority (IBAMA) adopted EPA rules for discharging drill cuttings from O&G operations. EPA method describes procedures to evaluate toxicity using Leptocheirus plumulosus. Despite being an exotic species, Brazilian laboratories keep L. plumulosus cultures. Otherwise, Grandidierella bonnieroides is widely distributed in Brazilian estuaries is successfully cultured and sensitive to many toxicants.

The present study was carried out to evaluate the effects of three non-aqueous drilling fluids (NAF) and two synthetic based drilling muds (SBM) spiked to natural sediment on the amphipods. Reference toxicant experiments were also performed using C16C18 internal olefin or a C16C18 internal olefin SBM of similar density.

Sediment was collected in Jabaquara beach, RJ and transferred to the laboratory in chilly bins. After sieving, it was kept at 4 ± 2 °C until spiking for no longer than 60 days. Spiking procedures and whole-sediment tests were set up following the methods described in EPA method 1644 and Brazilian Standards. Amphipods were exposed to 5 concentrations of SBM and NAF spiked sediment plus controls for 4 and 10 days, respectively, in static system.

In NAF tests using G. bonnieroides the average LC50 obtained were 3.53 (n= 7; SD=1.63; CV= 46.07%), 1.33 (n= 6; SD=0.69; CV= 52.15%) and 0.56 (n= 7; SD=0.24; CV= 42.69%) for olefin, ester and paraffin, respectively, while L. plumulosus showed an average LC50 of 1.66 (n= 6; SD=1.30; CV= 78.10%), 0.60 (n= 5; SD=0.22; CV=35.81%) and 0.26 (n= 6; SD=0.13; CV= 50.50%), respectively. The average LC50 obtained in SBM 1 (11.6 ppg) tests using G. bonnieroides was 139.78 (n= 3; SD= 69.47; CV= 49.70%) and for SBM 2 (9.9 ppg) the LC50 was 132.97, while L. plumulosus showed an average LC50 of 94.79 (n= 2; SD= 92.33; CV= 97.41%) LC50 of 34.82, respectively, for SBM1 and SBM2. In olefin tests using L. plumulosus, SBM 2 test using G. bonnieroides and SBM 1 tests using both species, STR ≤ 1 were obtained, meeting the EPA criteria for drilling cuttings discharge. Although G. bonnieroides has shown to be less sensitive than L. plumulosus to the NAF and SBM, the method using G. bonnieroides as test species demonstrated to be suitable for this purpose and presented similar variability than the same method using L. plumulosus.

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