Construction and demolition mineral-based waste impacts soil functioning and ecosystem services

Abstract

Over half of the world’s population live currently in urban areas with future projections estimating an increase to 68% by 2050, with a projected additional 1.2 million km2 of land to be converted to urban areas by 20301. Poor practice in the construction industry, lack of established processes and lack of practitioners to undertake surveys assessing soils health prior to a development, as well as loopholes in laws and policies are key factors affecting soil health during construction. Millions of tonnes of soils coming from construction sites are being disposed of in the landfill2 but 90% is inert. Although there are policies in place advising multiple recovery pathways for construction soil (e.g. agricultural and ecological improvement schemes)3 that should take precedence, the most widely used recovery pathway is for civil engineering purposes.     Urban soils are often overlooked but they play a major role in humans’ lives as the loss of soils functions can have not only disastrous consequences (e.g. loss of soil’s water infiltration function can cause increase flooding risk) but also huge financial repercussions. Construction inadvertently impacts soil health and functionality, due to soil loss, compaction, sealing, contamination, soil carbon loss, and soil biodiversity loss. In England and Wales the current approach for assessing the effects of a development on land and soil is restricted to the protection of biomass soil function for food, fibre and timber production,4 while other soil functions that are important in local, national and context of maintaining healthy ecosystems and mitigating climate change, are ignored.        To better understand whether construction waste contamination has a serious impact on soil functioning, we carried out a study which aimed to assess the impact of three major mineral-based construction materials (concrete, brick and plasterboard) on soil multifunctionality and ecosystem services under future climates. The materials were mixed with soil in 6 different addition treatments (5, 10, 20, 30, 40, and 50% material addition) and were maintained for 5 months at three different moisture contents (10, 25 and 50%). Soil moisture, total carbon and nitrogen, microbial biomass carbon and nitrogen, ammonium and nitrate, nitrogen mineralisation rate and microorganism community structure and abundance were measured the first and the last day of the experiment. Immediate responses were observed in all variables and were sustained throughout the duration of the experiment. Preliminary results show statistically significant stepwise reductions of plant available ammonium and nitrate as the materials’ additions were increased. pH increased immediately (Day 1) following the material additions, and although the stepwise pattern was lost, the values remained significantly higher than the controls (Day 150). Our results suggest that mineral-based construction materials have a significant impact on soil functioning which warrants further investigation if these soils are to be reused under circular economy principles.