Invisible pressures: A global review of unconventional coastal pollution sources and their environmental impacts.

Conventional sources of coastal pollution, such as industrial discharges, urban wastewater, agricultural runoff, and maritime operations, are well recognized in scientific literature and policy frameworks. These sources are routinely monitored, regulated, and quantified. In contrast, unconventional sources of coastal pollution remain largely absent from monitoring systems despite their growing environmental significance. They arise from diffuse, episodic, or culturally embedded human activities that are rarely addressed by existing regulations, even when they release significant pollutants into sensitive coastal and marine ecosystems. This review synthesizes global evidence of emerging and underrecognized pollution drivers, including religious rituals, informal economies, displacement crises, recreational events, and symbolic coastal practices. These drivers release plastics, chemicals, hydrocarbons, nutrients, and organic waste into habitats such as estuaries, coral reefs, dunes, seagrass beds, among others. Often, they operate without regulatory oversight or environmental assessment. We classify these pollution sources using a novel five-dimensional invisibility framework (cultural, behavioral, situational, institutional, and perceptual). This framework explains why many impactful activities remain unrecognized, under-reported, or unregulated. Cross-cutting patterns include spatial overlaps with protected areas, mismatches between pollutant release and detection, and disproportionate impacts on marginalized communities and critical ecosystem services. Governance blind spots, socio-political normalization, and disciplinary silos further exacerbate the invisibility of these sources. By integrating environmental science, coastal planning, and environmental justice perspectives, this review reframes the conceptual boundaries of marine pollution. It provides a typological, theoretical, and empirical basis for including unconventional sources in global monitoring and management strategies. Recognizing and integrating these drivers is essential for achieving Sustainable Development Goals and ensuring resilient, inclusive coastal governance.