PHOSPHORUS AND HEAVY METAL CONTENTS IN SMALL-SCALE COMPOSTING AREAS

Composting is an important tool for recycling and proper disposal of organic waste. However, in small-scale composting, where total soil sealing and leachate collection is not carried out, elements such as P, Cu, Zn, Cd, Cr, Ni and Pb may accumulate in soil. This study aimed to assess phosphorus and heavy metal contents in soils of areas used for small-scale food waste composting. In order to do this, we sampled soil depths of 0-5, 5-10, 10-20, 20-30 and 30-40 cm of four areas with composting times of 16, 12, 7 and 1 year, in addition to four reference areas. All the study areas are located in the city of Florianópolis, Santa Catarina state, Brazil. We determined available P, Cu and Zn contents and total Cu, Zn, Cd, Cr, Ni and Pb contents in the soil samples. We found that the production of organic compost directly on the soil generally promoted increases in available P contents, which were above acceptable environmental limits, especially at the uppermost soil layers. Still, the presence of Cu, Zn, Cd, Cr, Ni and Pb was not an environmental liability in the composting areas, as the contents found were below those recommended by legislation.