Analysis of Elevated Uranium and Impact of the Cotton Industry on Groundwaters in Benin, Africa

By detailing characteristics of groundwater in Benin through elemental signatures, the previous phase of this research sought to better understand the hydrogeology and spatial distribution of groundwater quality in Benin. Those data indicated elevated uranium concentrations in two wells in eastern Benin. In the current research effort it was hypothesized that the uranium present in groundwater is of natural geologic (and not anthropogenic) origin. It was further hypothesized, based on conversation with Dr. M Boukari of the University d'Abomey-Calavi, that the cotton agricultural industry has had some identifiable impact on groundwater quality. In order to provide data to assess both hypotheses, samples of groundwater, the associated filters, and various precipitation samples were collected in July 2002, and preserved for analysis. Quantitative elemental concentrations (elemental signatures) for the samples were acquired using Inductively Coupled Plasma (ICP) Spectrometry and specific ion probe techniques. These elemental parameters, in addition to latitude, longitude, temperature, pH, conductivity, and distance to cotton fields for each sample were compiled into a working matrix. Parameter- Benjamin Patrick Roope parameter plots were evaluated using an Exploratory Data Analysis (EDA) technique. Principle Component Analysis (PCA), Indicator Variable Analysis (IVA) and Cluster Analysis (CA) were also applied to the data. Conclusions were drawn about the characteristics of groundwater samples based on a full statistical perspective gained for each of the data sets. The results from the application of the EDA, IVA, and PCA methods support the stated hypothesis that the source of uranium in groundwater samples is geology-related. Records indicative of elevated concentrations of uranium in surface water in the eastern part of the country that predate allegations of human dumping also support the case. However, the same applied methods and similar literature searches provided little support of the assertion that groundwater is being contaminated by cotton farming (made by the second hypothesis). Although the major elements Ca and Na were noted at elevated concentrations near cotton fields, they were not definitively linked to agricultural practices or the use of pesticides. Future work will help identify the specific geologic formation(s) responsible for elevated uranium concentrations, and to subsequently conceive a remediation plan. Future work will also concentrate on conclusively determining the source of the elevated Ca and Na around cotton fields through soil sampling and testing.