Morphological deformations in <i>Chironomus plumosus</i> (Diptera: Chironomidae) at Santa Catarina River, Nuevo Leon, Mexico

The Santa Catarina River (SCR) is considered an urban forest within the Monterrey Metropolitan Area (MMA); however, the impacts of contaminants detected in this system on local fauna remain largely unknown. These contaminants include heavy metals, organic pollutants, and medical residues originating from stormwater runoff and clandestine discharges. This study evaluated the temporal stability of toxicity at the study site using the macroinvertebrate Chironomus plumosus as bioindicator determining the differential susceptibility of four anatomical structures (mentum, pecten epipharyngis, mandibles, and antennae). A Chi-square test confirmed the temporal stability of mentum deformities (28-48 %) across the sampling dates ( = 5.30, p = 0.151), indicating chronic and constant exposure. However, an Analysis of Variance (ANOVA) revealed highly significant differences in vulnerability among structures (F = 64.85, p < 0.001). The pecten epipharyngis exhibited the highest damage frequency (91.2 %), significantly exceeding the mentum (43.8 %), whereas the mandibles (7.0 %) and antennae (6.5 %) were the most conserved structures. Although the mentum is a reliable indicator, the pecten epipharyngis appears to exhibit a greater response to environmental stress, suggesting it as a more sensitive biomarker. It is recommended to adopt a multi-structural approach in future biomonitoring programs and to conduct tissue-level toxicological analyses to validate these findings.