International Journal of Advance Agricultural Research
ISSN: 2053-1265
Vol. 4(4), pp. 20-29, July 2016

Effect of long-term irrigation using treated wastewater on heavy metal contents of soils grown to Medicago sativa in the Kingdom of Bahrain

Ebrahim J. E.1, A. A. Salih2* and Asma Abahussain2

1Plant Wealth Directory, Manama, Kingdom of Bahrain.
2Department of Natural Resources and Environment, Arabian Gulf University, Manama, Kingdom of Bahrain.

*To whom correspondence should be addressed. E-mail:

Received 20 January, 2016; Received in revised form 15 February, 2016; Accepted 17 February, 2016.


Heavy metals, Alfalfa, Treated sewage effluent, Bahrain.

This study was conducted to evaluate the effect of long term use of irrigation with treated sewage effluents (TSE) on absorption and accumulation of some heavy metals and their possible contaminations of alfalfa crop and soil. Six farms irrigated with TSE were selected for the study in the Kingdom of Bahrain. Three of these farms were irrigated with TSE for less than 10 years while the rest were irrigated with TSE for more than 20 years. Samples of TSE were collected from each farm and soil samples were collected from alfalfa plots at two depths, (0-20 and 20-50 cm) in 3 replicates. A soil sample from outside the farm,was used as a control. Alfalfa samples were also collected. Heavy metal contents in TSE, soil and plant were determined. Salinity and pH in TSE, soil texture, Cation Exchange Capacity and organic matter were also determined. The results obtained indicate that the concentration of heavy metals in TSE did not exceed the international standards, except for Cadmium, which was double the allowable limit. Also, there were no significant differences caused by irrigation, in heavy metal concentration in the soil. However, the concentrations of Lead, Nickel and Chromium were lowered compared to un-irrigated soil. There were no significant differences (P=0.08) in heavy metals' concentrations between the two soil depths, except for Zinc and Cadmium (P=0.035) which showed higher concentrations in the upper and lower depths, respectively. Duration of irrigation with TSE did not significantly (P=0.05) affect heavy metals' concentrations in alfalfa except for Cadmium as its concentration was higher in alfalfa grown in soil irrigated for more than 20 years; yet, still within permissible limits. The correlations between soil properties and heavy metals’ contents were weak (R2=0.53) except between Calcium Carbonates and Cadmium, Nickel and Chromium, and between clay content and Chromium. It was concluded that long term irrigation with TSE did not cause an increase in heavy metals content in the soil. TSE can be used safely for irrigating fodder crops, with continuous monitoring of heavy metal content in the soil and the crops irrigated with it.

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