As part of the ecotoxicological tests on anuran tadpoles, the authors propose to study the sensitivity of different stages towards a nitrogenous compound frequently used in Morocco (Ammonium sulphate). For this purpose, the acute toxicity tests on tadpoles of two species (Bufo mauritanicus and Rana ridibunda) belonging to different stages of development were carried out. The lethal effects after 96 hours caused by the pollutant used as a reference (potassium dichromate) as well as ammonium sulfate increase with concentration and vary according to the stage of development. Significant differences were observed in the sensitivity of the tadpoles to pollutants according to the stage of development. The tadpoles belonging to the early stages of development (stage 24 according to Gosner, 1960) show greater acute effects on pollutants than the tadpoles belonging to the advanced stages of development (Stage 36 according to Gosner, 1960). After 96 hours, the lowest effective concentration (LOEC) is observed in the tadpoles belonging to the early stages of development (Stage 24 according to Gosner, 1960) in Rana ridibunda exposed just to the lowest concentration used (20 mg/l of ammonium sulphate). Therefore, ammonium sulfate may play a role in the local decline of amphibians.

Oued Nfifikh is among the least studied Moroccan rivers. Thus, the primary aim of this study was to shed light on the quality of this undervalued stream. Its downstream part is affected by one of the most crucial environmental issues. It receives the discharges of wastewater evacuated precariously without prior treatment, which might lead to the degradation of the overall ecological status of this fluvial hydrosystem. This research work aimed to study the physicochemical water quality downstream the river Nfifikh through a monthly monitoring of the physicochemical parameters' indicator of pollution, from August 2018 to July 2019. The results obtained show that the stream is exposed to high pollution which is mainly organic. Consequently, the wastewater represents a major cause of water quality degradation of this receiving environment: ecological and health impacts are therefore to be expected.