Impact of Caffeine on Aquatic Ecosystems: Assessing Trophic-Level Biological Responses

Abstract

This study evaluates the effects of caffeine (CAF) on the bacteria Aliivibrio fischeri, the microalga Raphidocelis subcapitata, the macrophyte Lemna minor, and the larvae of Chironomus riparius, aiming to understand its environmental impact and contribution to ecological risk assessment. Bioluminescence inhibition in A. fischeri (EC₅₀ = 998.5 mg/L) and growth inhibition in R. subcapitata and L. minor (EC₅₀ = 60.1 mg/L and EC₅₀ = 649.2 mg/L, respectively) were observed. For L. minor, reduced catalase (CAT) activity and non-linear responses in glutathione S-transferases (GSTs) were recorded. No significant changes were observed in proline, malondialdehyde (MDA), and pigment contents. In C. riparius, acute mortality (LC₅₀ = 644.5 mg/L) was observed, and growth was significantly affected after 10 days of CAF exposure (EC₅₀ = 81.62 mg/L for fresh biomass). After 10 days of exposure, there was an increase in CAT activity and thiobarbituric acid reactive substances, with TBARS levels both at concentrations ≥82.64 mg/L, and a decrease in GSTs (92.18 mg/L) and acetylcholinesterase (AChE) (≤62.09 mg/L) activities of C. riparius. The results show that CAF exposure affects organisms' metabolic and physiological functions, with varying sensitivities among species, potentially leading to ecological disturbances in aquatic ecosystems. The hazardous concentration for 5% of species was 4.42 mg/L. Long-term studies are necessary to understand the risk of caffeine under more realistic scenarios.

Keywords: ecotoxicology; emerging contaminant; freshwater ecosystems; individual and sub-individual responses; species sensitivity distribution.

Figure 1

Results for growth inhibition (mean ± SE) in R. subcapitata after 72 h of exposure to caffeine. ° stands for individual values (replicates). Grey shadows stand for significant differences compared to the control group (0 mg/L) (Dunnett’s test, p < 0.05). EC₅₀ value is also presented.

Figure 2

Results for biomass (fresh weight; mean ± SE) of L. minor after 7 days of exposure to caffeine. ° stands for individual values (replicates). Grey shadows stand for significant differences compared to the control group (0 mg/L) (Dunnett’s test, p < 0.05). EC₅₀ value is also presented.

Figure 3

Results for sub-individual parameters (mean ± SE) in L. minor after 7 days of exposure to caffeine. ° stands for individual values (replicates). Grey shadows stand for significant differences compared to the control group (0 mg/L) (Dunnett’s test, p < 0.05). The lack of results in proline content at the highest concentration is due to the absence of L. minor biomass.

Figure 4

Results for biochemical biomarkers (mean ± SE) in C. riparius larvae after 10 days of exposure to caffeine. ° stands for individual values (replicates). Grey shadows stand for significant differences between concentration and the control group (0 mg/L) (Dunnett’s test, p < 0.05).

Figure 5

Species sensitivity distribution (SSD) plots, showing the distribution of EC₅₀ values for organisms acutely exposed to CAF with 95% confidence intervals. Data were obtained from the literature, highlighted in bold and underlined for the present study (Brachionus calyciflorus [20]; Ceriodaphnia silvestrii [60]; Danio rerio¹ [59]; Danio rerio² [59]; Daphnia magna [28]; Desmodesmus subspicatus [61]; Pseudomonas putida [28]; Raphidocelis subcapitata [35]; Xenopus laevis [58]). Estimated hazardous concentrations for 5% of species (HC₅) and respective lower (LL) and upper (UL) values are presented.