Toxicity of representative organophosphate, organochlorine, phenylurea, dinitroaniline, carbamate, and viologen pesticides to the growth and survival of H. vulgaris, L. minor, and C. elegans

Abstract

Pesticides are commonly found in the environment and pose a risk to target and non-target species; therefore, employing a set of bioassays to rapidly assess the toxicity of these chemicals to diverse species is crucial. The toxicity of nine individual pesticides from organophosphate, organochlorine, phenylurea, dinitroaniline, carbamate, and viologen chemical classes and a mixture of all the compounds were tested in three bioassays (Hydra vulgaris, Lemna minor, and Caenorhabditis elegans) that represent plant, aquatic, and soil-dwelling species, respectively. Multiple endpoints related to growth and survival were measured for each model, and EC₁₀ and EC₅₀ values were derived for each endpoint to identify sensitivity patterns according to chemical classes and target organisms. L. minor had the lowest EC₁₀ and EC₅₀ values for seven and five of the individual pesticides, respectively. L. minor was also one to two orders of magnitude more sensitive to the mixture compared to H. vulgaris and C. elegans, where EC₅₀ values were calculated to be 0.00042, 0.0014, and 0.038 mM, respectively. H. vulgaris was the most sensitive species to the remaining individual pesticides, and C. elegans consistently ranked the least sensitive to all tested compounds. When comparing the EC₅₀ values across all pesticides, the endpoints of L. minor were correlated with each other while the endpoints measured in H. vulgaris and C. elegans were clustered together. While there was no apparent relationship between the chemical class of pesticide and toxicity, the compounds were more closely clustered based on target organisms (herbicide vs insecticide). The results of this study demonstrate that the combination of these plant, soil, and aquatic specie can serve as representative indicators of pesticide pollution in environmental samples.

Keywords: Battery of bioassays; EC10; EC50; Ecotoxicology; Herbicides; Insecticides.

Figure 1:

Toxicity of 2,4,6-trichlorophenol as shown by the morphological scores of H. vulgaris (A) and the corresponding dose-response curve at 92 hours of exposure (B). Data represent the average value from triplicate analysis ± the standard deviation. * Indicates a significant difference (p ≤ 0.05) from the vehicle control group after 92 hours of exposure.

Figure 2:

Toxicity of 2,4,6-trichlorophenol on the surface area (A), frond number (B), and chlorophyll content (C) during a 7 day exposure. Dose-response curves of the 7 day toxicity data for all 3 measured endpoints (D). Data represent the average value from triplicate analysis ± the standard deviation. * Indicates a significant difference (p ≤ 0.05) on day 7 of exposure compared to the vehicle control group.

Figure 3:

Toxicity of 2,4,6-trichlorophenol on the body length (A), nose touch response (B), and survival rate (C). The 48 hour toxicity data was used to create the dose-response graphs for the 3 endpoints (D). Data represent the average value from triplicate analysis ± the standard deviation. * Indicates a significant difference (p ≤ 0.05) after 48 hours of exposure compared to the vehicle control group.

Figure 4:

Distribution of EC₁₀ (A-B) and EC₅₀ (C-D) values (mM) for each pesticide between the measured endpoints for L. minor and C. elegans.

Figure 5:

Distribution of EC₁₀ (A) and EC₅₀ (B) (mM) values across all tested pesticides for the most sensitive endpoint in each bioassay.

Figure 6:

Clustering heatmap with distance matrix and dendrograms depicting the relationships between the measured endpoints for all model organisms based on their EC₁₀ (A) and EC₅₀ (B) values for all chemical exposures based on the Spearman correlation coefficient.

Figure 7:

Clustering heatmap with distance matrix and dendrograms depicting the comparison of EC₁₀ (A) and EC₅₀ (B) values of all the tested pesticides and mixture according to the Spearman correlation coefficient.