Terms Regression coefficient Standard error of the coefficient t-value P-value constant -280.353 5.533036 -50.669 0.000000 X1 1.233 0.047130 26.151 0.000000 X2 -0.013 0.000220 -61.134 0.000000 X3 0.694 0.046155 15.036 0.000000 X4 -0.024 0.000220 -109.843 0.000000 X1*X1 12.272 0.232115 52.871 0.000000 X2*X2 -1.204 0.005492 -219.326 0.000000 X3*X3 2.071 0.033977 60.965 0.000000 X4*X4 -0.003 0.000055 -61.816 0.000000 X1*X2 -0.008 0.000288 -26.511 0.000000 X1*X3 -0.022 0.001438 -15.385 0.000000 X1*X4 -0.000 0.000144 -0.782 0.446215a X2*X3 0.037 0.001438 25.468 0.000000 X2*X4 0.001 0.000144 5.998 0.000024 X3*X4 -0.000 0.000719 -0.608 0.551990a ainsignificant (P ≥ 0.05)

Table 7: Estimated regression coefficients for the lead biosorption onto Casuarina leaf powder.