This study focuses on the removal of organic pollutants present in landfill leachate (LL) using an adsorption process with activated carbon (AC) obtained from fish scales, and subsequently evaluates the reduction of toxicity in the wastewater obtained from the process. The AC obtained is a mesoporous material, with a cumulative pore area of 1.57 m(2) g(-1), Brunauer-Emmett-Teller (BET) of 1.8329 m(2) g(-1) and adsorption average pore width of 12.79833 nm. The maximum removal of pollutants was achieved at natural pH (6.71) of the LL, with a load of 3 g L-1, resulting in 60.1% colour and 37.3% chemical oxygen demand (COD). The rate of COD removal per g of AC increase had a maximum value of 5.6 at pH 10 when passing from 0.5 to 1 g AC. The lowest rate of 0.6 occurred for the same pH when it passed from 1 to 2 g AC. At pH 3 the second lowest rate of 3.3 was observed when passing from 2 to 3 g AC. At pH 3 there was always an increase in the rate as more AC was added. Conversely, at natural pH 6.71 the rate tended to decrease. At pH 10 the rate first decreased and then increased. At acidic pH, because it is the one with the lowest COD removal, it would be expected that by adding more AC the rate would continue to increase as there are easily accessible sites still available. Langmuir isotherms fitted adequately with the experimental data, providing an R-2 of 0.9657, which is consistent with a monolayer adsorption pattern. The LL before the adsorption process had an inhibition ratio of 20.4%, due to the fact that leachate can be toxic because of the presence of hazardous organic compounds. After adsorption processes at pH 6.71, the inhibition ratios were 16.9%, 13.8%, 12.2% and 10.9% at AC loads of 0.5, 1, 2 and 3 g L-1, respectively, due to decreasing COD and colour of the LL over the course of the treatment. It was observed that the reduction of the inhibition ratio was greater at higher loads of adsorbent. (c) 2020 Society of Chemical Industry