Graphitic carbon nitride (g-C3N4) has emerged as a promising nanomaterial due to its visible-light photocatalytic activity, chemical stability, and tunable electronic properties. While its applications in energy and environmental remediation are well-documented, understanding its ecotoxicological profile and environmental fate is critical for sustainable deployment. This review examines current research on the ecotoxicity and biodegradability of g-C3N4, focusing on exposure pathways, cellular effects, and regulatory considerations.

Exposure pathways of g-C3N4 in the environment primarily depend on its physicochemical properties, including particle size, surface chemistry, and dispersion stability. Studies indicate that g-C3N4 nanomaterials can enter aquatic systems through industrial effluents, wastewater discharge, or accidental spills during manufacturing. In terrestrial environments, soil contamination may occur through agricultural applications, such as photocatalytic soil remediation or controlled-release fertilizers. The mobility of g-C3N4 in water is influenced by pH and ionic strength, with aggregation observed under high salinity conditions, potentially reducing bioavailability. However, smaller particles or modified derivatives with enhanced colloidal stability may persist in water columns, increasing exposure risks to aquatic organisms.

Cellular and organismal responses to g-C3N4 exposure have been investigated across multiple trophic levels. In aquatic invertebrates like Daphnia magna, studies report low acute toxicity, with 48-hour LC50 values typically exceeding 100 mg/L for pristine g-C3N4. However, chronic exposure at sublethal concentrations has shown oxidative stress responses, including increased production of reactive oxygen species and altered antioxidant enzyme activities. Algal species exhibit growth inhibition at lower concentrations, with EC50 values ranging from 10-50 mg/L, likely due to shading effects and physical interference with photosynthesis rather than chemical toxicity. Vertebrate models, including zebrafish embryos, demonstrate limited bioaccumulation but show developmental abnormalities at high exposure doses, suggesting particle-dependent rather than ion-mediated toxicity.

The biodegradability of g-C3N4 remains a subject of ongoing research. The material's polymeric structure, consisting of tri-s-triazine units linked by nitrogen bridges, confers resistance to chemical degradation under ambient conditions. Photocatalytic self-degradation has been observed under prolonged UV-visible light exposure, where reactive species generated by the material itself contribute to partial breakdown of the framework. Microbial degradation appears limited, with few known species capable of metabolizing g-C3N4. Some studies report modest weight loss in compost environments, suggesting slow biodegradation over extended periods. Surface modifications, such as oxidation or incorporation of heteroatoms, may enhance biodegradability by introducing more labile functional groups.

Regulatory considerations for g-C3N4 nanomaterials are complicated by their variable formulations and lack of standardized testing protocols. Current frameworks for chemical risk assessment may not adequately address the unique properties of carbon nitride materials. Key challenges include defining appropriate dose metrics beyond mass concentration, accounting for photocatalytic activity in toxicity evaluations, and developing protocols for long-term environmental persistence studies. Some jurisdictions are considering grouping approaches based on material properties rather than case-by-case assessments, which could streamline regulation of g-C3N4 variants with similar characteristics.

Comparative analysis of g-C3N4 ecotoxicity relative to other carbon nanomaterials reveals distinct behavior patterns. Unlike graphene oxide or carbon nanotubes, g-C3N4 generally shows lower acute toxicity but comparable potential for chronic ecological impacts. The material's photocatalytic properties introduce unique considerations, as light exposure may simultaneously degrade pollutants while generating transient reactive species that could affect organisms. Lifecycle assessments suggest that the environmental footprint of g-C3N4 production and use may be offset by its applications in pollution control, but comprehensive analyses accounting for end-of-life scenarios are lacking.

Future research priorities should address several knowledge gaps. Standardized protocols for assessing g-C3N4 ecotoxicity across different environmental matrices are needed, along with long-term fate studies under realistic conditions. The development of structure-activity relationships could help predict ecological impacts based on material properties, enabling safer design of g-C3N4 nanomaterials. Improved analytical methods for tracking g-C3N4 in complex environmental samples would enhance exposure assessment capabilities. Multidisciplinary approaches combining materials science, ecotoxicology, and environmental chemistry will be essential for developing sustainable applications of this versatile nanomaterial.

The current body of research suggests that while g-C3N4 poses relatively low immediate ecological risks compared to some engineered nanomaterials, its persistence and potential for chronic effects warrant careful consideration in applications with high environmental release potential. Balanced against its beneficial uses in environmental remediation and renewable energy, the material exemplifies the need for application-specific risk-benefit analyses in nanotechnology development. Continued investigation into its environmental behavior will support evidence-based decision making for sustainable utilization of graphitic carbon nitride materials.