Trace Elements And Naturally Occurring Radioactive Materials In “Non-Traditional Fertilizers” Used In Ghana

Abstract

Fertilizers have been implicated for being contaminated with toxic trace elements and naturally occurring radioactive materials (NORMs) even though they are an indispensible component of our agriculture. This phenomenon of contamination has been investigated and established world-wide in various forms of fertilizers (i.e., granular or “traditional” type and liquid/powder or “non-traditional type”). In Ghana, the crop sub-sector has seen a gradual rise in the importation and use of „non-traditional fertilizers‟ which are applied to both the foliar parts and roots of plants. This notwithstanding, research on fertilizers has been largely skewed towards the “traditional” types, focusing principally on the subjects of yield, effects of application and their quality. This study was, therefore, undertaken to bridge the knowledge gap by investigating the levels of trace elements and NORMs found in the „non-traditional‟ fertilizers used in Ghana. The principal objective of the study was to investigate the suitability of the “non-traditional fertilizers” for agricultural purposes with respect to trace elements and NORMs contamination. Atomic Absorption Spectrometry and Instrumental Neutron Activation Analysis were employed to determine the trace elements (Cu, Zn, Fe, Na, Al, Br, Ni, Cd, As, Hg, Co, Pb, La, Mn, Si, Ca, Cl, S, K, Ba and V) and NORMs (238U, 232Th and 40K) concentrations in thirty-nine (39) fertilizer samples taken from two major agro-input hubs in the country (Kumasi-Kejetia and Accra). Multivariate statistical analyses (cluster analysis, principal component analysis and Pearson‟s correlation) were applied to the data obtained in order to identify possible sources of contamination, investigate sample/parameter affinities and groupings and for fingerprinting. The toxic trace element concentrations determined in all samples were found to be in the order Fe > Cu > Co > Cd > Cr > Ni > Pb > As > Hg. The study found most of the trace elements determined to be within limits set by international standards (Canada and Hungary and Washington State) except for Cu and Cd. However, all toxic trace elements were within allowable limits projected by the SUIT#25 model. Minimum guaranteed nutrients other than Nitrogen, Phosphorus and Potassium determined were largely found to be below levels set by the Part III of Act 803-Fertilizer Control and its Regulations even for the companies who declared the results on their labels. Generally, the activity concentrations in both the liquid and solid fertilizers were found to be in the order K-40 > Th-232 > U-238. The activity concentrations and hazard indices (Radium equivalent, Dose rate and Representative level) for the natural radionuclides U-238 and Th-232 were also found to be within safety limits and world average figures. However, the activity concentrations and computed hazard indices for K-40 in some products such as SKMKi were higher than the world average and standards set by United Nations Scientific Committee for Effect of Atomic Radiations (UNSCEAR). It was found from the Multivariate analysis that the toxic element Cd clustered with nutrients Zn and Fe, indicating that Cd might have been introduced during the process of nutrient addition to the fertilizers in the form of chelates. The natural radionuclides, 232Th and 238U also largely grouped together indicating that they are from a common source rock. The naturally occurring radioactive material K-40 also groups with Na, Br and partially with K indicating their common origin. The results from the cluster analysis, principal component analysis and Pearson‟s correlation show good agreement and suggest that all the liquid fertilizers can be grouped into five major groups with respect to their elemental contents. The CA, PCA and Pearson‟s correlation analysis for the solid samples also indicate similarities of 3 major clusters with sub-groupings and 5 components respectively. In conclusion, the dangers associated with the use of “non-traditional” fertilizers in Ghana are low with respect to toxic trace elements since their concentrations in the fertilizers are low. The potential for trace element accumulation in soil has also been found to be low. Furthermore, the liquid fertilizers are not radiologically significant whereas some solid fertilizers are significant due to their high activity concentrations and hazard indices. It is recommended that regulators continue to monitor imported fertilizers for toxic trace element content in order to ensure their safety for agriculture and environment at large. Further research and monitoring of trace elements and naturally occurring radioactive materials in other forms of fertilizers is required trace element and radiological data generation. The study has indicated the usefulness of multivariate analysis in contamination source determination and finger printing that may play a significant role in fertilizer quality monitoring.