Inhibition of the corrosion of zinc in 0.01 to 0.0 4 M H 2 SO 4 by erythromycin was studied using weight loss and hydrogen evolution methods. The results obtained indicate that erythromycin is a good adsorption inhibitor for the corrosion of zinc in H 2 SO 4 solutions. The inhibition efficiency of erythromycin increases with increasing concentration but decreases with increase in temperature. Thermodynamic and adsorption studies reveal that the adsorption of erythromycin on zinc surface is exothermic, spontaneous and is characterised with increasing degree of orderliness. The adsorption characteristics of the inhibitor are best described by the Langmuir adsorption model. From the variation of inhibition efficiency with temperature and the calculated values of the activation and free energies (which are within the limits expected for physical adsorption), we propose that the adsorption of erythromycin on zinc surface is consistent with the mechanism of physical adsorption.

Heavy metals concentrations were determined using Atomic Absorption Spectrophotometer (UNICAM SOLAR 32).Gas chromatography-flame ionization detector instrument was used in the detection and evaluation of levels of TPH while measurements of PAHs (total) concentration were performed with the aid of Chromatography mass spectrometer. Pollution indices such as contamination factor (CF) and geoaccumulation index (I geo ) as well as established guidelines of some selected countries and organizations on site contamination were used to compare results. Soil samples were obtained in triplicates and in soil depths of [10][11][12][13][14][15][16][17][18][19][20] Cu, As, Pb, Cd and Hg ranged between 112.30 to 202.10 mg/kg, 0.90 to 5.80 mg/kg, 0.08 to 2.50 mg/kg,16.10 to 32.3 mg/kg, 1.90 to 11.78 mg/kg and 0.30 to 1.66 mg/kg with mean concentrations of 157. 00, 3.84, 1.40, 22.30, 7.02 and 0.89 mg/kg respectively in soils of NNPC depot. Results of analysis of PAHs and TPH ranged from 6.30 to 7.40 mg/kg and 5120.50 to 24902.23 mg/kg respectively. Values of geo-accumulation index revealed that the study site was contaminated with Pb, Hg and Cd (toxic metals). Established guidelines on assessment of site contamination soils from several countries used to compare this result demonstrated high levels of contamination of soils from NNPC depot Aba by Hg, Pb, Cd, PAHs and TPH compounds. The decreasing order of heavy metals concentration in the study site is presented as follows: Zn>Pb>Cd>Cu>As>Hg.

The corrosion of zinc in 0.01 to 0.04 M H 2 SO 4 was studied using gravimetric and gasometric methods of monitoring corrosion. The results obtained indicate that clarithromycin is a good adsorption inhibitor for the corrosion of zinc in H 2 SO 4 . The inhibition efficiency of clarithromycin increases with increasing concentration but decreases with increasing temperature. There was no significant difference between the inhibition efficiencies of clarithromycin obtained at various concentrations of H 2 SO 4 (P>0.5), but values of inhibition efficiency tend to decrease with increasing concentration of the acid. The adsorption of clarithromycin on zinc surface is endothermic, spontaneous and is best described by Langmuir adsorption isotherm. Calculated values of activation energies and free energies of adsorption indicate that the adsorption of clarithromycin on zinc surface supports the mechanism of physical adsorption.

Inhibition of the corrosion of zinc in various concentrations (0.01 to 0.05 M) of H 2 SO 4 was studied using weight loss and hydrogen evolution methods of monitoring corrosion. The results revealed that various concentrations of azithromycin (0.0001 to 0.0005 M) inhibited the corrosion of zinc in H 2 SO 4 at different temperatures (303 to 333 K). The concentration of H 2 SO 4 did not exert significant impact on the inhibition efficiency of azithromycin, but inhibition efficiencies were found to decrease with increase in the concentration of the inhibitor. Values of inhibition efficiency obtained from the weight loss measurements correlated strongly with those obtained from the hydrogen evolution measurements. The activation energies for the corrosion of zinc inhibited by azithromycin were higher than the values obtained for the blank. Thermodynamic data revealed that the adsorption of azithromycin on the surface of zinc was endothermic (values of enthalpies of adsorption were positive), spontaneous (values of free energies of adsorption were negative) and was consistent with the adsorption model of Langmuir.

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