Associating contaminant risks with land use changes over time

Throughout the Pacific Islands land use changes have resulted in intensified contaminant impacts that threaten the integrity of coastal ecosystems and communities. Pu'uloa (Pearl Harbor) in Hawai'i offers a model system in which to explore these changes. Once a center of food production, famous for its abundant marine resources, numerous loko i'a (Hawaiian fishponds), calm waters, and flowing streams, the area has been permanently altered. Land use change over two centuries (1825-2023) was reconstructed by georeferencing 38 historical maps and integrating these with spatially explicit environmental contamination data compiled from agency reports, peer-reviewed studies, and gray literature. 200 years of land use transitions are visualized and linked to contaminant profiles in Pu'uloa, which revealed three central findings. 1) From the late 19th century onward, Pu'uloa shifted from largely undeveloped lands to plantation agriculture and then to extensive post-World War II urban development. 2) Metals and legacy pesticides emerged as the most prevalent contaminants, reflecting the region's land use history, with Honouliuli showing the highest concentrations due to sugar plantations and military activities. 3) Toxic burden risk is disproportionately borne by Native Hawaiian and Black residents. Situating contamination within a spatial-temporal land-use history clarifies where risks are concentrated and who and what are most affected. This evidence can guide remediation and management, support restoration of culturally significant places, and inform the revitalization of associated practices. The framework is transferable to other islands in Hawai'i and other islands globally that are confronting similar land-use legacies.