Int. J. Environ. Res. Public Health 2009, 6 2400 carried out within a temperature range of 10 to 80 °C, achieved by heating to a designated temperature of 40, 60 or 80 °C in a Clifton thermostatic water bath (NE 1 Range, U.K.), from the room temperature of 29 °C. A temperature of 10 °C was achieved by the addition of ice blocks to the water bath at room temperature and at each reaction temperature, new sets of samples were used. On attaining the desired temperature, the mixture was immediately agitated on an electrically operated Edmund Bühler shaker (Model KS 10/A) at 300 rpm for 2 h, allowed to cool, centrifuged at 2,100 rpm for 5 minutes and then filtered through a 0.45 µm filter. Experiments were carried out on three replicates, hence, a total of 90 samples were worked on, which consisted of five different sets of nine compost samples derived from the turned -series and another five sets of nine samples derived from unturned-series. The filtrates were then digested using aqua-regia (3:1 HNO3-HCl) in a fume cupboard. Metal concentrations (Cu, Zn, Cd and Pb) in the filtered digests were measured using the atomic absorption spectrophotometer. The metal water- extractability from the compost bulk at a given temperature was evaluated by dividing the water- soluble metal fraction by the total metal concentration and multiplying by 100. Using linear regression models derived for the metals, water-extractable fractions in relation to temperature regimes from 0.1 of 1.5 °C at a regular interval of 0.1 were simulated. 2.3. Statistics 3. Results Data were subjected to descriptive statistics using SPSS 15.0 for Windows (SPSS Inc., Chicago, IL, USA) and linear regression models were also obtained for simulation in addition to correlations used to establish relationships. Table 1 shows that generally, the respective total metal concentration in bulk compost (mg·kg-1) and water-soluble metal fractions (mg·kg-1) ranged from 0.83 to 6.00; 0.018 to 0.200 for Zn, 0.13 to 7.50; 0.004 to 0.163 for Pb, 0.70 to 0.82 ; 0.014 to 0.076 for Cu and 0.13 to 0.22; 0.001 to 0.012 for Cd. The total metal concentrations were all within the maximum acceptable limits for compost material. Results also showed that the water-extractable metal fractions did not exceed 10% of the total metal concentration of the bulk compost, which corresponded to 0.30 to 6.63% for Zn, 0.09 to 7.51% for Pb, 1.83 to 9.29% for Cu and 0.67 to 9.23% for Cd. The line graphs (Figure 1), demonstrating the trend for water-extractable metal concentrations of the composted organic wastes with increasing temperature regime, showed that Zn in all cases gave a dome bell shape, indicating that a maximum value was attained after which a decline was observed. Pb was almost similar to Zn in all the systems but differed in Figure 3 for agricultural wastes (CAGW-T), where a steady increase with temperature was obtained. The other two metals (Cu and Cd) exhibited a more steady increase.