Assessment of the developmental and neurotoxicity of the mosquito control larvicide, pyriproxyfen, using embryonic zebrafish

Abstract

In 2014, as an attempt to address the Zika health crisis by controlling the mosquito population, Brazil took the unprecedented action of applying a chemical larvicide, pyriproxyfen, to drinking water sources. The World Health Organization has established an acceptable daily intake of pyriproxyfen to be 100 μg per kg of body weight per day, but studies have demonstrated that at elevated doses (>5000 mg/kg), there are adverse effects in mice, rats and dogs. To better understand the potential developmental toxicity of pyriproxyfen, we utilized the embryonic zebrafish. Our results demonstrate that the concentration resulting in 50% of animals presenting adverse morphological effects (EC50), including craniofacial defects, was 5.2 μM for daily renewal exposure, and above this concentration, adverse behavioral effects were also observed in animals that followed a static exposure regimen. Thus, zebrafish data suggest that the developmental toxicity of pyriproxyfen may not be limited to insects.

Keywords: Behavior; Development; Morphology defects; Neurotoxicology; Pyriproxyfen; Zebrafish; Zika.

Figure 1. Comparison of developmental exposure to pyriproxyfen after (A) static exposure and (B) daily renewal

For the first panel of each chemical (Aggregated Entropy: AggE), the gray line represents the significant threshold of AggE by concentration, which is determined by summation cross all the endpoints; black line is the cumulative summation of chemical-associated AggE morphological effects by concentration, and the red colored points represents those that exceed the threshold. The other panels represent the 18 morphological endpoints assessed. The 4 endpoints measured at 24 hpf are not shown as there was no statistical significance. Each red dot represents a significant (above threshold) incidence count at a given concentration. A Fisher’s Exact test was used to identify the significance threshold.

Figure 2

Figure 3. Larval photomotor response to alternating light and dark cycles after static exposure

Data are reported as mean ± standard deviation at each second time bin. The number of contributing animals (originally n=32) for 0, 0.0064, 0.064, 0.64, 6.4, and 64 μM is 28, 24, 24, 28, 25, and 15, respectively.