Int. J. Environ. Res. Public Health 2009, 6 2399 Assessment of temperature effects on readily available heavy metals from composts would give insight and understanding of their bioavailability with increasing global temperature, which in turn will facilitate the control of potential phytotoxicity and subsequent ecological hazards of organic fertilizers arising from global warming. This study was therefore designed to investigate (i) the effect of temperature changes on water-extractable heavy metals (Zn, Cu, Cd and Pb) concentrations from composted wastes (ii) relating them to the total metal concentrations in the bulk compost materials and temperature variations and (iii) prediction over a gradual temperature rise from 0.1 to 1.5 °C via simulation models. 2. Materials and Methods 2.1. Composting Domestic wastes materials (kitchen wastes and other compostable household wastes, excluding human wastes) collectively called household wastes (HHW); agricultural wastes consisting of farmyard crop residues (AGW), commercial and institutional wastes, including outdoor market wastes, office and food wastes from fast-food centers, collectively called municipal solid wastes (MSW) were used in this study. All the materials were source segregated and collected from the city of Abeokuta, south-west Nigeria. Each subset of the organic solid wastes (HHW, AGW or MSW) was mixed with sawdust at an organic waste to sawdust material ratio of 7:1 (w/w). The resulting bulk of HHW, AGW or MSW was then mixed with cow dung (CD) at a material/CD ratio 1:3 (w/w). The turning schedule adopted was once in three days and systems were replicated three times in 30 L black plastic composters, which were raised 30 cm above the ground. The wastes composted within 42 days but was allowed 35 days more for stabilization. The described experimental procedure was repeated but in this case, the turning schedule was omitted, hence, composting proceeded without any form of turning after the initial material mix and the experimental set up was also replicated three times in 30 L black composters. In all, 18 composts were produced (nine for the turned-series and nine for the unturned-series). The composted wastes were denoted as CHHW, CAGW and CMSW. Total metal concentrations (Cu, Zn, Cd and Pb) of the bulk compost were determined by digesting 0.1 g sample directly with aqua- regia (3:1 HNO3-HCl) and the metal concentrations in the digests were measured using a calibrated Bulk Model 210 flame atomic absorption spectrophotometer (Buck Scientific, USA) using air-acetylene-oxygen gas mixture. Reagent blanks were determined and standard additions gave recoveries of 98.97 ± 0.21 for Cu, 99.56 ±0.28 for Zn, 99.23 ±0.22 for Cd and 98.89 ±0.23 for Pb. 2.2. Batch Extraction Experiment at Different Temperature Regimes The modified method of [18] was adopted using a solid-water ratio of 1:25. Air-dried and ground sample (2 g) from each of the 18 bulk compost materials was transferred to a 50 mL graduated plastic sample bottle, previously rinsed with acidified (1% HNO3) deionised water procured from the Analytical Laboratory of the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria. This was followed by the addition of 50 mL of non-acidified deionized water. The experiments were