Temp. (oC) Cu 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 *∆ **∆ 0.1, 1.5 Zn 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 *∆ **∆ 0.1, 1.5 0.00157 0.00164 0.00171 0.00178 0.00185 0.00192 0.00199 0.00206 0.00213 0.00220 0.00227 0.00234 0.00241 0.00248 0.00255 0.00007 62.42% 0.09095 0.09090 0.09085 0.09080 0.09075 0.09070 0.09065 0.09060 0.09055 0.09050 0.09045 0.09040 0.09035 0.09030 0.09025 -0.00005 -0.77% -0.00075 -0.00066 -0.00057 -0.00048 -0.00039 -0.00030 -0.00021 -0.00012 -0.00003 -0.00006 0.00015 0.00024 0.00033 0.00042 0.00051 0.00009 168% 0.09627 0.09624 0.09623 0.09618 0.09615 0.09612 0.09609 0.09606 0.09603 0.09600 0.09597 0.09594 0.09591 0.09588 0.09585 -0.00003 -0.44% Int. J. Environ. Res. Public Health 2009, 6 Table 4. Potential water-extractable Cu and Zn (mg·kg-1) from composted wastes of Nigerian origin relative to incremental temperature rise by 0.1 °C. Compost_HHW-T Compost_HH W-U Compost_AGW-T Compost_AGW-U Compost_MSW-T Compost_MSW-U Y = 0.0007x + 0.0015 Y = 0.0009x – 0.00084 Y = 0.001x – 0.0177 Y = 6E-05x + 0.0102 Y = 0.0007x – 0.0018 Y = 0.0006x + 0.0031 -0.00173 -0.00166 -0.00159 -0.00152 -0.00145 -0.00138 -0.00131 -0.00124 -0.00117 -0.00110 -0.00103 -0.00096 -0.00089 -0.00082 -0.00075 0.00007 56.65% 0.08624 0.08618 0.08612 0.08606 0.08600 0.08594 0.08588 0.08582 0.08576 0.08570 0.08564 0.08558 0.08552 0.08546 0.08540 -0.00006 -0.97% 2404 0.00316 0.00322 0.00328 0.00334 0.00340 0.00346 0.00352 0.00358 0.00364 0.00370 0.00376 0.00382 0.00388 0.00394 0.00400 0.00006 26.58 0.09891 0.09882 0.09873 0.09864 0.09855 0.09846 0.09837 0.09828 0.09819 0.09810 0.09801 0.09792 0.09783 0.09774 0.09765 -0.00009 -1.27% -0.0176 -0.0175 -0.0174 -0.0173 -0.0172 -0.0171 -0.0170 -0.0169 -0.0168 -0.0167 -0.0166 -0.0165 -0.0164 -0.0163 -0.0162 0.0001 7.95% 0.053091 0.053082 0.053073 0.053064 0.053055 0.053046 0.053037 0.053028 0.053019 0.053010 0.053001 0.052992 0.052983 0.052974 0.052965 -0.000009 -0.24% 0.010206 0.010212 0.010218 0.010224 0.010230 0.010236 0.010242 0.010248 0.010254 0.010260 0.010266 0.010272 0.010278 0.010284 0.010290 0.000006 0.82% 0.06906 0.06902 0.06898 0.06894 0.06890 0.06886 0.06882 0.06878 0.06874 0.06870 0.06866 0.06862 0.06858 0.06854 0.06850 -0.00004 -0.81% Y = –0.0005x + 0.091 Y = –0.0003x + 0.0963 Y = –9E-05x + 0.0531 Y = –0.0004x + 0.0691 Y = –0.0006x + 0.0863 Y = –0.0009x + 0.099 HHW = household waste, AGW = Agricultural waste, MSW = municipal solid waste, U = unturned series, T = turned series, *∆ = incremental change by 0.1 °C rise, **∆ = percentage change between 0.1 and 1.5 °C. 4. Discussion Results from this study revealed that the degree of temperature effect on water extractability of heavy metals from the bulk composts was dependent on metal type, compost formulation and waste type. There is no readily available data on this subject for comparison. However, previous works on water-extractable trace metals from composted organic matter, carried out at prevailing temperature values, gave < 0.2% for Pb, about 2% for Cu, undetectable for Cd [3] while Sawhney et al. [19] reported that the water extractable fractions of Cd, Cr, Ni and Pb were about 3% each, relative to the bulk compost material. Water-extractability of the metals was attributed to variations in their affinity towards nonhumic and humic substances. A significant correlation of water-extractable Cu and water-extractable humic compound was reported [3]. Literature has reported immobilization of metals within the compost matrix arising from metal-humic complex formation. Humic substances, especially humic acids are complex polyfunctional mixtures in humified organic materials that play significant role in trace metal bioavailability [8,20-25].