A permeable reactive barrier (PRB) is an in-situ remediation structure placed across the path of a contaminant plume, allowing groundwater to pass through while reactive media inside the barrier degrade or immobilise contaminants. In this dataset, PRB filings are classified primarily under C02F (water and wastewater treatment, 83.3% of the 972 records) and B09C (soil and contaminated land reclamation, 33.8%). Claims typically cover either the reactive material itself — zero-valent iron, nanoparticle-activated oxidants, bioremediation microbes — or the physical barrier construction, such as layered geotextile and casing designs.

The ranking is drawn from 100 assignees returned by the dataset, not a top-50 or top-100 industry list. The single leading assignee holds 23 of the 972 records, but the top 5 combined hold only 10.1% of the field and the top 10 hold 16.7%, meaning most activity comes from a long tail of organisations filing only a handful of records each. This spread includes environmental remediation contractors, research institutes and industrial firms, several of them Chinese state-affiliated environmental science institutes.

Filings rose from 22 in 2017 to a peak of 83 in 2021, then fell to 61 by 2024, a -27% change over that three-year span. The 2025 and 2026 figures are lower still, but publication typically lags actual filing by around 18 months, so those final years are incomplete rather than proof of a slowdown. Judged on complete years only, the field has passed its 2021 peak but remains well above 2017 levels.

China's receiving office accounts for 572 of the filings tracked, far ahead of the United States at 101, South Korea at 78, the WIPO PCT route at 47, the European Patent Office at 36 and Australia at 30. This concentration means prior art searches and freedom-to-operate assessments that only cover US and European filings will miss the majority of documented activity in this field.

The most-cited records in this corpus cover foundational reactive-media chemistry rather than recent structural variations: zero-valent iron bioremediation of contaminated aquifers, general aquifer remediation methods, and nanoparticle-activated oxidant systems, several cited well over 100 times within this dataset. A new filing proposing reactive-media chemistry should expect dense prior art in these areas; a filing focused on barrier construction, layering or deployment method is likely to face a thinner citation trail.