Potentially toxic metals in irrigation water, soil, and vegetables and their health risks using Monte Carlo models.

Food safety has become a serious global concern because of the accumulation of potentially toxic metals (PTMs) in crops cultivated on contaminated agricultural soils. Amongst these toxic elements, arsenic (As), cadmium (Cd), chromium (Cr), and lead (Pb) receive worldwide attention because of their ability to cause deleterious health effects. Thus, an assessment of these toxic metals in the soils, irrigation waters, and the most widely consumed vegetables in Nigeria; Spinach (Amaranthushybridus), and Cabbage (Brassica oleracea) was evaluated using inductively coupled plasma-optical emission spectroscopy (ICP-OES). The mean concentration (measured in mg kg-1) of the PTMs in the soils was in the sequence Cr (81.77) > Pb(19.91) > As(13.23) > Cd(3.25), exceeding the WHO recommended values in all cases. This contamination was corroborated by the pollution evaluation indices. The concentrations (measured in mg l-1) of the PTMs in the irrigation water followed a similar pattern i.e. Cr(1.87) > Pb(1.65) > As(0.85) > Cd(0.20). All the PTMs being studied, were found in the vegetables with Cr (5.37 and 5.88) having the highest concentration, followed by Pb (3.57 and 4.33), and As (1.09 and 1.67), while Cd (0.48 and 1.04) had the lowest concentration (all measured in mg kg-1) for cabbage and spinach, respectively. The concentration of the toxic metals was higher in spinach than in cabbage, which may be due to the redistribution of the greater proportion of the metals above the ground tissue, caused by the bioavailability of metals in the aqueous phase. Expectedly, the hazard index (HI),and carcinogenic risk values of spinach were higher than that of cabbage. This implies that spinach poses potentially higher health risks. Similarly, the Monte Carlo simulation results reveal that the 5th percentile, 95th percentile, and 50th percentile of the cumulative probability of cancer risks due to the consumption of these vegetables exceeds the acceptable range of 1.00E-6 and 1.00E-4. Thus, the probable risk of a cancerous effect is high, and necessary remedial actions are recommended.

Assessment of Radium Equivalent Activity and Total Annual Effective Dose in Cassava cultivated around Ewekoro Cement Factory.

In this study, cassava tubers cultivated in the Ewekoro cement area were investigated with the aid of Hyper Pure Germanium (HPGe) detector in order to assess the radionuclide content. Twenty-seven (27) samples of both arable soil and cassava tubers were studied at different sites to the epicenter of the mining activity. The results revealed the highest activity concentrations of K-40, Ra-226, and Th-232 to be 194.10, 63.92, and 76.90 Bq/kg, respectively, in soil to be at site 1, which was 50 m away from the cement mining site. Similarly, cassava reported the highest activity concentrations of 228.15 and 81.50 Bq/kg for K-40 and Ra-226, respectively, at sites 2, which was 150 m away from the mining site. However, the highest value of Th-232 in cassava was noted in site 1. Also, the highest values of Raeq for arable soil and cassava tubers were estimated to be 188.84 Bq/kg and 199.89 Bq/kg at site 1 and site 2, respectively. All the above results were higher than the recommended safe limits by a factor of 2. Moreover, the Total Annual Effective Dose of exposure by oral ingestion of cassava tubers for different age groups revealed children to have the highest level of exposure with the highest mean value of 7.98 mSv. This is followed by adults and infants, which reported 5.66 and 5.38 mSv, respectively, all at site 2. This result is far greater than the recommended safe limits of 1 mSv. Therefore, the results of the total averages of annual effective doses due to consumption of the three natural radionuclides in cassava tubers and other products from it by adults, children, and infants were found to be above the average annual ingestion radiation dose due to natural sources. Further statistical analysis of the results showed significant differences between sites 1 and 2 and between sites 1 and 3, where there was no statistically significant difference between sites 2 and 3.

Heavy metal contamination of selected mining fields in North-Central Nigeria.

This study evaluates the causes, concentration and the associated health risks of selected heavy metals (HMs) in soil samples collected from beryllium and gold mining fields in Nigeria. The samples of soil were collected manually and analysed by means of Atomic Absorption Spectrophotometry (AAS). Seventy-two (72) samples were analysed which presented varying degrees of concentration of the selected HMs. The analysed HMs are Chromium (Cr), Arsenic (As), Iron (Fe), Cadmium (Cd), Nickel (Ni), Manganese (Mn), Magnesium (Mg), Zinc (Zn), Copper (Cu) and Lead (Pb). Deterministic and stochastic approaches were explore to examine the human health risks. The evaluated Hazard Indices (HI) for the investigated mining locations are < 1, the recommended threshold provided by United State Environmental Protection Agency (USEPA) for acceptable non-cancer risk. The estimated cancer risk levels for the mining locations exceeds the acceptable range of 1.00E-6 and 1.00E-4.•Thus, the mining is making significant contribution to HMs pollution, which is dangerous human health.•However, the Monte Carlo simulation (MCS) reveals that the 95th, 50th and 5th percentiles of the cumulative probability of the cancer risks are within the acceptable range.•This work will be useful for decision makers in mitigating heavy metals contamination due to mining activities.

Soil-to-plant transfer of 40K, 238U and 232Th and radiological risk assessment of selected mining sites in Nigeria.

One of the major route through which humans are exposed to ionizing radiation is via food chain, which is consequent of soil-to-plant transfer of radionuclides. This work reported the activity concentrations of 40K, 238U and 232Th in samples of water, soil and guinea corn grains collected from Beryllium and Gold mining sites in Kwara, Nigeria. In-situ measurements at approximately 1 m in the air was carried out using a well-calibrated portable Gamma Spectrometer (Super Spec RS-125), while the soil, water and the guinea corn samples were analyzed using a '3 × 3' inch lead-shielded NaI (Tl) detector. The measured activity concentrations of the natural radionuclides in the soil from both mines are lower than the in-situ measurements. This was attributed to the contribution from other terrestrial materials on-site. The estimated mean transfer factors (TFs) for 40K, 238U and 232Th are 0.21, 0.17 and 0.31, and 0.46, 0.19 and 0.28 respectively for the Beryllium and Gold mining sites. While the TFs for 238U and 232Th exceeded the mean value of 0.0062 and 0.0021 for 238U and 232Th respectively, the TFs for 40K are well below the 0.74 for cereals grains provided by International Atomic Energy Agency (IAEA). The radiation impact assessment using the Monte Carlo simulations reveals values that were generally less than the global average values provided by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). Hence, the risk of cancer inducement due to radiation exposure is within the acceptable limits for both mining sites.

Toxicology of Heavy Metals to Subsurface Lithofacies and Drillers during Drilling of Hydrocarbon Wells.

This study investigates the toxicological effects of heavy metals on lithofacies of the subsurface in a drilled hydrocarbon well as well as, to the drilling crew and people in an environment. The pollution levels of selected heavy metals were considered alongside their ecological effects during dry and wet seasons. The health hazard potential of human exposures to the metals, were estimated in terms of intensity and time using the USEPA recommended model. The heavy metal concentration for each layer decreased across the lithofacies as follows; Layer 5> Layer 4> Layer 3> Layer 2> Layer 1. The average concentrations of the heavy metals present in the samples obtained from the formation zone, varied significantly and decreased in the order of Al> Zn> Ni> Pb> Cr> Cu> Cd> As> Hg. The highest concentration of Al, Cu, and Zn in this present study were within the maximum allowable limits whereas, those of As, Cd, Hg and Ni were all above their maximum allowable limits. Among the transition metals analysed, the maximum mean daily dose of Pb (9.18 × 10-6 mg/kg/d) and Cr (1.42 × 10-6 mg/kg/d) were confirmed susceptible to human carcinogens and environmental toxins. The estimated hazard quotient shows that the dermal pathway is the most likely route via which the drilling crew and people in the environment can get contaminated. The cancer risk values for the Pb (7.72 × 10-4), Cd (1.35 × 10-1), Ni (9.97 × 10-3), As (1.50 × 10-1) and Cr (3.16 × 10-3) are all above the acceptable values. The cancer risk contribution for each metal was in the order of As> Cd> Ni> Cr> Pb. Layer 5 had the maximum Geo-accumulation index for the heavy metals considered. This higher Geo-accumulation index noted at the depth in Layer 5 may be attributed to the effect of water basin with turbidity currents, deltas, and shallow marine sediment deposits with storm impacted conditions. Also, the pollution from lead (Pb) in the dry season was maximum with an Igeo value> 5 for all the lithofacies considered because of the low background concentration of the metal. During the wet season, the heavy metal pollution rate was moderate for Zn whereas, it was extremely polluted with respect to Pb. The ecological risk potential of Pb shows that the associated ecological risks range from 536 - 664 in the wet season (i.e. extremely strong) and 2810 - 3480 in dry season (extremely strong). The high level of Pb pollution found in the area at such shallow depth may be due to the sedimentary folds possibly caused by the full spectrum of metamorphic rocks and primary flow structures at shallow depths. This was used to identify the environmental sensitivities of the heavy metals during the dry and wet seasons.

Assessment of naturally occurring radiation in lithofacies of oil field in Niger Delta region and its possible health implications.

The accumulation and increase in radionuclide activities of NORMs beyond permissible levels, will lead to health hazards and environmental damages if proper measures are not taken to control their occurrence as well as protect the lives of drillers and the environment. Therefore, evaluations and risk assessments of subsurface lithofacies is inevitable in order to protect people and the environment. Lack of existing Federal environmental regulations to address the presence of NORMs in oil and gas exploration activities in Nigeria, gives credence to this study. However, before these regulations can be developed, adequate research knowledge is needed to better understand the occurrence and distribution of Norms in subsurface lithofacies, as well as quantify the hazards posed by these NORMs to the people in the environment. This study then investigates the occurrence of natural radiation in lithofacies of an oil field region in Niger-Delta area using Hyper Germanium (HPGe) detector. Six (6) samples of different subsurface layers of lithofacies were collected during drilling, and analyzed. The results showed that the measured activity concentration of 238U decreased as the depth increased; the activity concentration of 232Th ranged between 11.8 ± 9.29 Bq/kg and 23.1 ± 8.43 Bq/kg, while the activity concentration of 4 K ranged from 161.8 Bq/kg to 245.4 Bq/kg. The estimated radiological risks such as absorbed dose rates, annual effective dose rates, radium equivalent index, external hazard index and internal hazard index were determined. The mean values for the estimated radiological parameters were 12.32 nGyh-1, 15.1049 Svy-1, 44.7720 Bqkg-1, 0.1209 and 0.1318 respectively. The gamma index estimated for the samples used were within the standard values recommended by Unscear, 2000. Significantly, this study reveals a distinctive decrease in 232Th activity with depth within the area under consideration. Based on the compared results, the measured radioactive concentrations and estimated radiological risks were below international reference values.

Geo-investigation on groundwater control in some parts of Ogun state using data from Shuttle Radar Topography Mission and vertical electrical soundings.

Groundwater is a vital natural resource that plays a significant function in sustainability of living things on earth. Its exploration requires special skill for optimum exploitation. Shuttle Radar Topography Mission (SRTM)and Vertical Electrical Sounding (VES) were used to detectthe stratigraphy and subsurface structures controlling the groundwater system around Iju - Ota, Ogun State, Southwestern Nigeria. Nineteen (19) VES points were carried out where there were dense concentrations of lineaments and interconnected to establish the connection of the observed lineaments with groundwater occurrence in the study area using Schlumberger array, with electrode spacing of AB/2 varying from 180 to 320 m. The analysis of SRTM data revealedthe dominating structural NE-SW and NW-SE trends, which control aquifer structure. The geoelectrical parameters from the VES results were used to map the stratigraphic sequences in the study area. Six (6) units that comprisethe topsoil, lateritic clay, clayey sand, mudstone, sand (main aquifer), and shale or clay were identified in the study area. The aquiferous unit around Iju - Ota axis ranged from 30 to 80 m. Theextracted from the hill shaded SRTM data and the result of VES revealed that the thickness of the aquifer is as a result of interconnectivity of the lineaments observed in the SRTM data suggesting that the groundwater occurrence in the study area is chiefly controlled by these fractures.

Radiological and toxicity risk exposures of oil based mud: health implication on drilling crew in Niger Delta.

Naturally occurring radioactive materials (NORMs) and the presence of toxic metals in drilling fluids/their additives have raised research interests in recent times owing to the risks associated with the exposure times for drillers of petroleum wells. In this study, two drilling fluids A and B were formulated, while two other Mud Samples C and D were obtained from drilled shale and shale-sand formation zones. All four fluids were collected and analyzed for the presence of radioactive and heavy metals. Lead (Pb), mercury (Hg), cadmium Cd), zinc (Zn), chromium (Cr), aluminum (Al), arsenic (As), nickel (Ni), and copper (Cu) were detected in the mud samples. The heavy metal contents of the mud samples are in the following decreasing order of magnitude Hg > Pb > Cd > Cr. In Samples A-D, Hg, Pb, Cr, and Cd were found to have significant concentrations, and the concentrations of these metals increased in the mud samples after they were used for drilling. The concentration of Hg was above the permissible limit. Also, the concentrations of Pb, Cu, As, and Al found in Mud Samples A and B can cause skin irritations over long-term exposures, while Cd, Hg, Zn, and Ni present in the samples were within levels that can cause lung infections or immune breakdown when ingested over long periods. The quantities of Cd, Hg, and Cu detected in Mud Samples C and D can cause skin irritations over long-term exposures, while those of As, Zn, Ni, and Al were seen to have the potential to cause dermal infections/diseases. Based on the results obtained, the cancer risk for the drilling crew lies within 1.1 × 10-3 - 7.7 × 10-3 HQ. The highest dose rate, radium release, and external hazard index were obtained for Mud Sample C whose radium equivalent was judged to be far below the critical safe limit for the drillers. The radium equivalent activity for the two field mud samples (C and D) were estimated to be 27.467 and 22.978 Bq kg-1, respectively, which is the maximum activity obtained for the analyzed samples. The maximum radium equivalent activity for Mud Sample C was estimated as 27.48 Bq kg-1 with a corresponding external hazard index of 0.7. Based on the analysis, there is a significant correlation between the concentration of heavy metals and the radionuclides found in the mud samples.

Comparison between experimental and satellite temperature datasets in Covenant University.

This article contains the ground and satellite meteorological data sets of clear-sky temperature events for five years (2012-2016) in Covenant University, Ota, Ogun State, Nigeria. The satellite data were obtained from Atmospheric Infrared Sounder (AIRS) while the ground data information were acquired from Davis weather station data logger-vantage pro2. These data were acquired from propagation study that used same location (Lat: 6.67°N and Long: 3.23°E) for both satellite data and radiometer directed along the same path by providing information about the temperature. The data sets were assessed and evaluated by means of a descriptive statistics. There was perfect agreement between the two data. The peak temperature events occurs between the months of November and April for the five years of observation for both Ota and AIRS Satellite. The data from this article can be used for further studies on non-rainy attenuation effect in the study area.

Health risk assessment of heavy metal variability in sachet water sold in Ado-Odo Ota, South-Western Nigeria.

The sales of sachet water (SW), also known as "pure water" (PW), in Nigeria is a lucrative business. It serves many people, especially low-income earners, by providing a more affordable access to safe drinking water when compared with table water. However, some of the producers of SW do not effectively treat raw water before packaging them for sale. This study investigates the presence and concentrations of heavy metals, such as chromium (Cr), iron (Fe), manganese (Mn), copper (Cu), aluminum (Al), and zinc (Zn) in some samples of SW sold within Ota, Ogun State, Nigeria. Samples of SW from nine different producers were purchased for four consecutive weeks and analyzed to determine the concentrations of these heavy metals in them. Furthermore, health risk indicators, such as chronic daily intake (CDI) and health risk indices (HRI) for children and adults, were calculated separately. The metal concentrations were compared with allowable limits set by the World Health Organization (WHO), Nigerian Industrial Standard (NIS), and the United States Environmental Protection Agency (US EPA). High concentrations of Cr, Fe, and Al were found in all the nine samples and exceeded the maximum allowable limits (MAL) of all the standards considered. However, the concentrations of Zn, Mn, and Cu were within permissible limits. The HRIs of heavy metals were in the order of Cu > Fe > Zn > Mn > Al > Cr, but since the standard limits set for some metals were exceeded, proper and effective treatment is required to safeguard the health of consumers.