Y1 Progress report | Yusuph Aron Kafula

Towards Resilient Freshwater Ecosystems: Pinpointing Interactive Effects of Light, Temperature and Pesticide Pollution on The Structure and Functioning of Temporary Ponds

To predict and mitigate the impact of pesticide pollution on freshwater ecosystems, pesticides are typically subjected to ecological risk assessments that feed into environmental policies and regulations. As part of the first steps in conducting such assessments, the acute toxicity of a pesticide is determined through single-species exposure tests with model organisms representing three trophic levels: primary producers (algae), primary consumers (invertebrate grazers), and secondary consumers (fish). Typical model organisms that are used for these tests are Acutodesmus obliquus (green algae) and Anabaena sp. (cyanobacteria) as primary producers, Daphnia magna (water fleas) as primary consumers, and zebrafish (Danio rerio) as secondary consumers.

In contrast, in many countries in Sub-Saharan Africa, registration of new agricultural chemicals (pesticides) relies solely on their efficacy against targeted pests, without independent ecological risk assessments tailored to the often specific environmental conditions of these countries. Instead, ecological and unintended effects are derived from manufacturers' or companies' dossiers, which are based on traditional toxicity tests with established model species. Importantly, however, relying solely on these classic models can lead to unexpected effects when their sensitivity does not reflect that of local species, which are often adapted to very different environmental conditions.

Indeed, our previous study confirmed that local invertebrate species from temporary ponds can be more sensitive than traditional models. By extension, how stressors affect the structure of temporary pond communities and the overall ecological functioning of these systems remains unknown. With the increasing intensity of additional anthropogenic stressors (e.g., rising global temperatures and constant exposure to artificial light), the sensitivities of local species may be even higher, such that extrapolations from traditional toxicity tests with classic model species may no longer be adequately protective.

This project, therefore, aims to increase our understanding of the impacts of temperature increase, pesticide exposure, and light pollution on temporary pond systems, focusing on characterising their short– and long-term effects under separate and combined exposure scenarios.

In the first year of the project, the focus was on

• Assessing the acute toxicity of cypermethrin, abamectin and chlorpyrifos under different temperature and light exposure scenarios on selected temporary pond species.

• Assessing the combined effects of sub-lethal cypermethrin, abamectin and chlorpyrifos, temperature and prolonged light exposure on life history and physiological traits of temporary pond species. Following an extended drought and erratic rainfall, collecting experimental animals became a challenge. However, I was able to map ponds, and test organisms were subsequently collected.

• Producing the majority of the consumables required in my exposure tests. With sustained connections with other researchers in the field globally, I obtained a postdoctoral mobility fellowship at the University of Namur, Belgium, where I further refined my research protocols in the Laboratory of Adaptive Biodynamics, which conducts similar research using different models. I ran full-scale ecotoxicological tests from the end of 2025 to March 2026.

I have conducted toxicity tests on a temporary-pond ostracod (Cypridopsis africana) using two commercially available insecticide formulations containing cypermethrin and chlorpyrifos as active ingredients. The toxicity of chemical contaminants on freshwater organisms has been well established under controlled single-stressor experimental setups. However, their toxicity under simultaneous exposure to environmental stressors (e.g. prolonged lighting and elevated temperature) remains poorly understood. Here, we tested the toxicity of two commonly used insecticides, chlorpyrifos and cypermethrin, under elevated temperatures and prolonged artificial lighting in the ostracod Cypridopsis africana.

For chlorpyrifos, seven nominal concentrations (0 – 8.1 µg/l) were crossed with two temperature conditions (27 °C vs 31 °C) and two light regimes (24h:0h light: dark vs 12h:12h light: dark). For cypermethrin, similar temperature and light conditions were crossed with eight nominal concentrations (0 – 48.64 µg/l). After 48 hours of exposure, the lowest observed mortalities under elevated temperature and prolonged lighting occurred at environmentally relevant concentrations of both chlorpyrifos (0.1 µg/l) and cypermethrin (1.52 µg/l). Following an increase in temperature by +4 °C and prolonged lighting (24h:0h light: dark), both chlorpyrifos and cypermethrin LC50 decreased by up to 60%. These findings confirm that the toxicity of the studied insecticides is modulated by temperature, at the projected global level by the year 2100, and by artificial lighting at a presumed safe intensity (10 lux). Therefore, when estimating ecological risks, realistic lighting and temperature scenarios should be considered when deriving predicted no-effect concentrations to protect non-target species. These findings confirm that the toxicity of the studied insecticides is modulated by temperature, at the global level projected for the year 2100, and by artificial lighting. Therefore, ecological risk estimates for adequately protecting non-target species should consider realistic light and temperature scenarios in predicting no-effect concentrations.

Currently, I am conducting a full-scale toxicity test of cypermethrin on the fish Oreochromis niloticus.

An understanding of transdisciplinary research in my study has shifted to ensuring co-definition of the research problem and success metrics with stakeholders, in my case, farmers, the National Environmental Management Council, Local government authorities, and fisheries groups. Therefore, the work is oriented towards real management decisions, not only scientific discovery but also the building of integrated teams with people who actively work in aquatic toxicology, ecology, data modelling, and social/decision sciences. It also enabled iterative learning loops in which pilot results update sampling and modelling, while stakeholders help interpret trade-offs, communicate risks, and refine mitigation options based on local settings.

Annual report submitted by Dr Yusuph Aron Kafula

(summarised for publication by Heidi Sonnekus for the FAR-LeaF Programme)