Behaviour and biochemical responses of the marine clam Ruditapes decussatus exposed to phosphogypsum.

The phosphate fertilizer and phosphoric acid industries increase phosphogypsum levels in the aquatic environment leading to various disturbing effects. In the present work, we investigated the bio-uptake of heavy metals following the exposure of Ruditapes decussatus to three concentrations of phosphogypsum, 10, 20 and 40 g kg-1, under laboratory conditions. The amounts of Zn, Cd and Pb in several organs of the clam Ruditapes decussatus was determined using inductively coupled plasma optical emission spectroscopy (ICP-OES). Phosphogypsum acts on the behaviour of R. decussatus by increasing filtration rates. The most treatments showed significantly higher metal concentration in all tissues than the controls. Excavation behaviour was altered in treated bivalves compared to controls. The filtration rate (FR) of clams was significantly affected by exposure to phosphogypsum. Indeed, FR increased in clams exposed to phosphogypsum. Phosphogypsum has decreased SOD, CAT and MDA activities in the gills, digestive gland, gonad and muscles according to the concentration indicating a defense against oxidative stress. AChE was significantly inhibited in clams from all the sampling sites compared to controls. The considered parameters could be useful biomarkers for the evaluation of phosphogypsum toxicity in threatened biota. This study was conducted as part of a further investigation into the use of a comprehensive approach combining chemical and biological parameters to assess the health status of the Gabes gulf population. It provides the first database referring to phosphogypsum contamination and its biological effect in this ecosystem. The present study fills in a needed gap in the literature.

Microplastics in freshwater environment: the first evaluation in sediments from seven water streams surrounding the lagoon of Bizerte (Northern Tunisia).

Microplastic (MP) concentrations were determined, for the first time, in surface sediment of seven streams around the lagoon of Bizerte (Northern Tunisia), using a saturated NaCl flotation technique. Microplastics were categorised according to type, colour and size using a stereoscopic microscope. Results showed that all sediment samples contained MPs. The greatest MP abundance was observed at Jedara stream (6920 ± 395.98 items kg-1 dry weight), while the lowest mean value was 2340 ± 227.15 items kg-1 dry weight at Khima stream. The highest numbers of MPs were from streams near populated areas and municipal and industrial effluent discharges. Samples were made up entirely of secondary MPs mainly fibres, followed by fragments and films. The predominant colours were as follows: black > clear > white > red > blue > green > yellow for fibres, white > blue > black > red for fragments and red > white > clear > green > blue = black for films. Microplastic particles in the samples ranged from 0.2 to 5 mm in length. FTIR analysis revealed that the abundant polymers were polypropylene and polyethylene. This work contributes to the growing evidence that MP contamination is widespread even in freshwater ecosystems and provides a baseline for future studies and risk assessments.

Effect of carbaryl (carbamate insecticide) on acetylcholinesterase activity of two strains of Daphnia magna (Crustacea, Cladocera).

The present study was designed to investigate the effect of carbaryl (carbamate insecticide) on the acetylcholinesterase activity in two strains (same clone A) of the crustacean cladoceran Daphnia magna. Four carbaryl concentrations (0.4, 0.9, 1.8 and 3.7 µg L(-1)) were compared against control AChE activity. Our results showed that after 48 h of carbaryl exposure, all treatments induced a significant decrease of AChE activities whatever the two considered strains. However, different responses were registered in terms of lowest observed effect concentrations (LOEC: 0.4 µg L(-1) for strain 1 and 0.9 µg L(-1) for strains 2) revealing differences in sensitivity among the two tested strains of D. magna. These results suggest that after carbaryl exposure, the AChE activity responses can be also used as a biomarker of susceptibility. Moreover, our results show that strain1 is less sensitive than strain 2 in terms of IC50-48 h of AChE activity. Comparing the EC50-48 h of standard ecotoxicity test and IC50-48 h of AChE inhibition, there is the same order of sensitivity with both strains.