Physicochemical Characteristics and Quantification of Heavy Metals in Compost of Municipal Organic Solid Waste in High Andean Areas of Peru

The study evaluated the quality of compost made from municipal organic solid waste at the CEPASC plant in Concepción, Junín (3414 m above sea level). Compost was analyzed at two maturation stages: 60 days (Compost A) and 120 days (Compost B), using international protocols (TMECC) and advanced techniques such as inductively coupled plasma mass spectrometry (ICP–MS) to characterize physicochemical parameters and heavy metal concentrations. The results showed significant differences between the two composts. Compost A stood out for its higher quality as an organic amendment, with higher levels of organic matter (37.82%) and total nitrogen (1.77%). Compost B, on the other hand, showed indicators of greater maturity due to a lower C/N ratio (14.74), although it presented higher salinity. Both composts met the pH (slightly alkaline) and electrical conductivity ranges required by the regulations of Peru, Chile, and Mexico, guaranteeing that they will not damage roots due to excess salts. However, Compost B did not reach the minimum moisture content required by Peruvian standards. Regarding the quantification of metals, a critical situation was revealed concerning food safety; arsenic (As) proved to be the most serious contaminant, exceeding permitted limits in Compost B by double and reaching a geoaccumulation index considered “strong.” Zinc (Zn) also exceeded most international standards, representing a phytotoxicity risk. In conclusion, although the products fulfill basic nutritional functions, the contamination load index (CLI > 1) and the “very high” environmental risk suggest that the source residues are deteriorated. Their use in agriculture for human consumption should be restricted or handled with extreme caution due to the bioaccumulation of metals such as As, cadmium, and lead. This study presents one of the first reports on high‐altitude composting.