Restore brownfield sites and reduce heavy metal exposure in Peru

Mining is the mainstay of Peru's national economy: the country ranks second in global copper, silver, and zinc production, third for lead, and eighth for gold, with concessions covering nearly 15% of the national territory (AFD, 2023). While this sector generates around 12% of GDP and 15% of public revenue (AFD, 2023), it also has a negative environmental impact, with over 6,000 abandoned or inactive sites in 2025 that pose a long-term risk to public health, ecosystems, and water resources (Chappuis, 2020).

In 2023, around 29% of the Peruvian population, or almost 10 million people, were living in poverty (INEI, 2023), a figure rising to 40% in mining regions such as Cajamarca, Cerro de Pasco, and Puno. These communities are also exposed to high levels of heavy metals (lead, arsenic and aluminum) in the soil and water, increasing the risks of neurotoxicity, cancer, and health problems in pregnant women and children (Piñeiro et al., 2021).

Under the "polluter pays" principle, site operators are reponsible for remediation, but the government intervenes through AMSAC for high-risk mining sites or when a responsible party has not been identified. AMSAC currently manages a portfolio of around 65 rehabilitation projects across 11 of the country's 24 regions, with an annual budget of approximately 140 million soles (~€35.3 million), and is responsible for a total of 1,194 mining environmental liabilities (PAM). Faced with this mammoth task, AMSAC aims to develop innovative and cost-effective solutions for restoring contaminated sites, based on biological technologies and the circular economy.

BioBoost addresses two common issues with former mining areas: management of neutralized sludge generated from acid mine drainage treatment and the high cost of healthy topsoil. Rather than decontaminating entire plots of land, the BioBoost solution transforms this residual sludge into a fertile topsoil layer to cover contaminated soils. This topsoil is produced by combining biochar, organic matter, sand, and manure, to stabilize metals at safe levels and restore the necessary soil structure and fertility to support plant life (AMSAC; Piñeiro et al., 2021).

The innovation of this project lies in its operational feasibility: the sludge is continuously produced on-site, and transformed through a relatively simple process (mixing, aeration and conditioning), using locally-sourced enrichment materials to reduce transport and supply costs (AFD, 2023).

Having already been tested in the laboratory, FID funding will be used to trial the solution at four sites (Pasco, Junín, Lima, and Huancavelica).

The project aims to demonstrate that transforming mining sludge into topsoil is an operationally-feasible rehabilitation model that could be incorporated into national programs.

The main deliverables are:

• Produce enriched topsoil for use on pilot plots and validate its capacity to support plant life (germination and growth tests on two local grass species);
• Assess the environmental impact under real-world conditions: change in pH, heavy metal concentrations, soil parameters, biological dynamics, and plant cover;
• Reduce pollutant dispersion by limiting soil erosion and direct contact with contaminated soil;
• Reduce population exposure to heavy metals and the associated health risks, while prioritizing the most vulnerable communities;
• Produce a documented and replicable protocol, with quality control measures, for use at other mining sites;
• Boost community involvement by launching training, production, application, and monitoring initiatives, with attention to equitable participation between men and women.

Over the long term, AMSAC could use BioBoost to rehabilitate more sites on the same budget, by replacing sludge storage and the import of topsoil with this circular model, that could be rolled out to other mining regions across Peru, and potentially to other countries facing similar challenges.