Limited data have been published on the chemistry of urban soils and vegetation in the Philippines. The aim of this study is to quantify the concentrations of heavy metals (i.e., Cr, Ni, Cu, Zn, and Pb) in soils and vegetation in the urban landscape of Quezon City, Philippines, and to elucidate the relationships between soil properties and the concentration of heavy metals pertaining to different land uses [i.e., protected forest (LM), park and wildlife area (PA), landfill (PL), urban poor residential and industrial areas (RA), and commercial areas (CA)]. Soil (0-15 cm) and senescent plant leaves were collected and were analyzed for soil properties and heavy metal concentrations. Results revealed that the concentrations of heavy metals (i.e., Cr, Ni, Cu, Zn, and Pb) in urban soils were higher in areas where anthropogenic activities or disturbance (PL, RA, and CA) were dominant as compared to the less disturbed areas (LM and PA). Organic matter and available phosphorous were strongly correlated with heavy metal concentrations, suggesting that heavy metal concentrations were primarily controlled by these soil properties. The average foliar heavy metal concentrations varied, ranging from 0 to 0.4 mg/kg for Cd, 0-10 mg/kg for Cr, 2-22 mg/kg for Cu, 0-5 mg/kg for Pb, and 11-250 mg/kg for Zn. The concentrations of Cd and Cr exceeded the critical threshold concentrations in some plants. Leaves of plants growing in PL (i.e., landfill) showed the highest levels of heavy metal contamination. Our results revealed that anthropogenic activities and disturbance caused by the rapid urbanization of the city are major contributors to the heavy metal accumulation and persistence in the soils in these areas.

Sludge generated from wastewater treatment facilities has been applied in agriculture as soil conditioners. However, the incomplete and/or inappropriate treatment of wastewater may result in sludge that may still contain heavy metals, helminth ova, and coliforms posing a risk to both humans and the environment. This study assessed various pretreatment techniques such as co-composting, vermicomposting, and a combination of these on sludge samples to remove heavy metals (cadmium and mercury), helminth ova, and coliforms. Physico-chemical and biological analyses were used to compare untreated (i.e. raw) and treated sludge samples. The results showed that for the raw sludge, mercury (4.02 +/– 0.17 mg/kg) and cadmium (6.30 +/– 0.48 mg/kg) exceeded the limits specified under the Philippine National Standard (PNS) for Organic Soil Amendments of 2 mg/kg and 5 mg/kg, respectively. Laboratory examinations also revealed the presence of helminth ova (5 ova/g) and coliforms (10 CFU/g) in the samples. Sludge samples subjected to a combination of co-composting and vermicomposting resulted in the elimination of mercury and a significant reduction in cadmium concentration from 6.30 mg/kg to 1.12 mg/kg. No helminth ova were observed in the samples after further drying. However, both treated and untreated sludge samples had low nutrient content. The study highlights the need for raising public awareness and educating farmers on the potential risks associated with the use of raw sludge for agriculture.