Pesticide concentration in three selected fish species and human health risk in the Lake Tana sub-basin, Ethiopia.

Pesticide use has increased in the Lake Tana sub-basin due to increased agricultural activity, potentially endangering nontargeted organisms. To assess its potential impact on fish health and fish-consuming human populations, pesticide concentrations in the fillet and liver tissue of three fish species, namely Labeobarbus megastoma, Labeobarbus tsanensis, and Oreochromis niloticus, were investigated in Lake Tana. Fish samples were taken from the lake near the rivers of Ribb and Gumara, which flow through agricultural areas where considerable amounts of pesticides have been applied. A total of 96 fish samples were collected. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) revealed the presence of ten pesticides. Pyrimethanil was frequently detected in 96% of liver and 65% of fillet samples at a median concentration of 33.9 µg kg-1 and 19.7 µg kg-1, respectively. The highest concentration of pyrimethanil was found in L. megastoma (1850.0 µg kg-1). Labeobarbus megastoma also had the highest concentration of oxamyl (507.0 µg kg-1) and flazasulfuron (60.1 µg kg-1) detected in the liver tissue. The highest concentration of carbaryl (56.5 µg kg-1) was found in the liver tissue of O. niloticus. Fish tissue samples from the two study sites contained pyrimethanil, oxamyl, carbaryl, and flazasulfuron. Only pyrimethanil showed a statistically significant difference between the two sites and the species L. megastoma and L. tsanensis. The amounts of pesticides found in the fish species pose no direct risk to the health of fish consumer human population. However, the results show that the lake ecosystem needs immediate attention and regular monitoring of the rising pesticide usage in the lake watershed.

Olive mill waste biochar: a promising soil amendment for metal immobilization in contaminated soils.

The potential use of biochar from olive mill waste for in situ remediation of metal contaminated soils was evaluated. Biochar was mixed with metal contaminated soil originating from the vicinity of an old zinc smelter. Soil-biochar mixtures were equilibrated for 30 and 90 days. At these time points, Ca(NO3)2 exchangeable metals were determined, and effects of the biochar amendment on soil toxicity were investigated using plants, bacteria, and earthworms. Bean (Phaseolus vulgaris) growth, metal content, antioxidative enzymes activities, and soluble protein contents were determined. Furthermore, effects on soil microbial communities (activity, diversity, richness) were examined using Biolog ECOplates. After 120 days of soil-biochar equilibration, effects on weight and reproduction of Eisenia foetida were evaluated. With increasing biochar application rate and equilibration period, Ca(NO3)2 exchangeable metals decreased, and growth of bean plants improved; leaf metal contents reduced, the activities of antioxidative stress enzymes decreased, and soluble protein contents increased. Soil microbial activity, richness, and diversity were augmented. Earthworm mortality lowered, and their growth and reproduction showed increasing trends.