Ecotoxicological Effects of Imidacloprid and Lambda-Cyhalothrin (Insecticide) on Tadpoles of the African Common Toad, Amietophrynus Regularis (Reuss, 1833) (Amphibia: Bufonidae)

Agriculture is the main activity carried out in Cameroon and pesticide use is believed to be a common rule for its success. Most of the farms are situated close to water bodies, thus constituting a potential risk to non-target aquatic organisms. Declines of amphibian populations have been a worldwide issue of concern for the scientific community during the last several decades. The aim of this study was to assess the effects of an insecticide used by local farmers in Buea on amphibians. Parastar 40WP® which is constituted of imidacloprid + lambda-cyhalothrin a commonly used insecticide was applied on tadpoles of the African common toad Amietophrynus regularis (Reuss, 1833) in a static renewal experiment. The acute toxicity test was carried out after a range finding test from which seven test concentrations were selected. These concentrations were 0.0025mg/l, 0.005mg/l, 0.01mg/l, 0.05mg/l, 0.1mg/l, 0.5mg/l and 0.2mg/l. Signs of toxicity such as hyperactive symptoms, loss of balance, motionlessness and death were recorded. A varying degree of mortality (dose-dependent) was noticed during the test. On the contrary, no such toxicity signs and mortality occurred in the control, indicating that they were caused by the test substance. The 24h LC50 was 3.66mg/l, which is less than the recommended application dose (125mg/l). Products constituted of imidacloprid and lambda-cyhalothrin should therefore be handled with care and far from water bodies because of their potential to cause harm to non-target aquatic biota

Assessment of Chemical Pollution With Routine Pesticides Using PRIMET, a Pesticide Risk Model in the Benoe Stream in the South-West Region of Cameroon

Widespread extensive and improper application of pesticides may pose risk to aquatic ecosystem and affect non-target organisms. This study aimed at assessing chemical pollution with pesticides using the PRIMET (Pesticides Risks in the tropics to Man, Environment and Trade) model in the Benoe stream. Ecotoxicological data on pesticides, pesticide and water physico-chemistry were used as input parameters. Water parameters were measured monthly for 06 months in 08 sampling points along the stream. Pesticide characteristics were obtained from the Pesticides Properties Data Base (PPDB) and the PRIMET software. The risk assessment was done for 44 active ingredients used in the area and whose ecotoxicological and physico-chemical data were available. Water parameters significantly (p<0.05) varied across seasons. Based on the Exposure Toxicity Ratio (ETR) and the Predicted Exposure Concentration (PEC), the model predicted 09 pesticides to pose a definite acute risk (ETR>100), seven to pose an acute possible risk (1≤ETR≤100) and 28 to pose no risk (ETR<1). Cadusafos (ETR=5200, PEC=39µg/l) was the most risky pesticide while imazalil (ETR=0.0002, PEC=0.0053µg/l) was the least risky compound. Cypermethrin was predicted to pose both definite acute risk to water and possible chronic risk to fish, water and Daphnia. Seven active ingredients were predicted to pose possible chronic risk to Daphnia. Pesticide used in plantations near water bodies is a threat to the aquatic ecosystem augmented in case of misuse. Bioaccumulation potential and impact of these compounds on water quality and biota community structure should be examined