Peri-urban agriculture of food crops is practiced in many slum areas in developing countries. This often uses waste water whose levels of essential and non-essential elements are largely unknown but would be feared to contaminate soils, consequently exposing man to associated health risks. Inhabitants in Kibera slum, Nairobi City practice these growing kales, amaranthus, arrowroots, and spinach. Health risk assessment was done using daily intake of metals (DIM), target hazard quotient (THQ) and incremental lifetime cancer risk (ILCR). Atomic absorption spectroscopy was employed for elemental analysis. The levels of essential elements ranged as follows; Mn 91.04 - 374.44, Mg 261.28 - 532.96, Fe 350.74 - 1273.68, and Zn 1.18 - 6.3 μg/g per dry weight were found to be below the recommended limits by FAO/WHO. Non-essential elements ranged as follows; Cr 1.15 - 4.32 and Pb 0.14 - 0.91 μg/g above the EU recommendation. DIM of Fe 5.81 - 27.61 and Mn 1.97 - 8.12 μg/g is above the recommended daily intake amounts. THQ values for Mn and Fe were more than unit. THQ values for non-essential elements were generally below unit. ILCR showed that from lead alone 73 people (0.043% of 0.17M residents) are likely to develop cancer. There are foreseen health risks associated with consumption of food crops grown in Kibera slum that requires immediate address.
According to the World economic Report on Food Crises [
The health risk assessment has been done using a number of tools/indices such as Daily Intake of Metals (DIM), Target Hazard Quotient (THQ) [
Studies have reported on the assessment of the health risks of metals in food crops. Zhuang and co-workers [
The health risk indices DIM, THQ and ILCR are calculated as per Equations (1)-(3), respectively [
DIM = [ M ] × k × l (1)
where;
[M]: Metal concentration in plant (mg/kg);
k: conversion factor of fresh plant weight consumed to dry weight estimated as 0.085;
l: average daily intake of food crop estimated at 0.255 kg/day per adult.
THQ = EF × FD × DIM RfD × W × T (2)
where;
EF: exposure frequency (183.5 days/year);
FD: exposure duration (66.5 years, the average lifespan);
DIM: in mg/person/day);
RfD: oral reference dose (mg/kg/day);
W: average adult body weight (74 kg);
T: average of time for non-carcinogens [
ILCR is obtained using the CSF as shown in Equation (3). The CSF is the risk produced by a lifetime average dose of 1 mg∙kg−1 BW∙day−1 and is contaminant specific [
ILCR = CDI × CSF (3)
where;
CSF: cancer slope factor (0.085 for Pb);
CDI (mg∙kg−1 BW∙day−1); lifetime average daily dose of exposure to the chemical contaminant.
The CDI value was computed using Equation (4)
CDI = EDI × EF r × ED tot AT (4)
where;
EDI: estimated daily intake of metal via ingestion;
EFr: exposure frequency (365 days/year);
EDtot: exposure duration of 66.5 years average lifetime for Kenyans;
AT: averaging time for non-carcinogens.
The total cancer risk of exposure to multiple contaminants was assumed to be the sum of the individual metal incremental risks.
EDI of metals determined using Equation (5).
EDI = C metal × W food B w (5)
where;
Cmetal: concentration of metal in the contaminated vegetable (mg/kg);
Wfood: average daily consumption of vegetable in this region;
Bw : average body weight (74 kg).
Research has shown that soil, water, and food crops in Kibera slum have high levels of essential and non-essential elements [
The study focused on analyzing samples from gardens in Kibera slum in one dry season, using the result to calculate the DIM, THQ and ILCR indices and hence assess the potential health risk.
Kibera is in the south-west part of Nairobi, latitude −1˚18'60''S and longitude of 36˚46'99''E it is about 6.6 kilometers from the city center. Much of its southern border is bound by the Nairobi River and the Nairobi Dam. The Nairobi dam is an artificial lake that is currently used as a dumpsite. Kibera slum is divided into villages, which include Makina, Laini Saba, Lindi, Gatwekera, Soweto East, and Kianda [
The Kenya Population and Housing Census Report [
to peri-urban farming of kales, Dhania, cowpeas, onions, amaranthus, spinach and arrowroots for nutritional benefits. The sampling sites include Gatwekera, Kisumu Ndogo, Kianda, Lindi, Laini Saba and Siranga in Kibera slum coded as U001 - U006 respectively.
Five grams of Amaranths, Kales, Arrowroots, and Spinach samples were randomnly collected from six gardens in Kibera Slum by randomized design. For the control, 5 g of arrowroots, kales, amaranths, and spinach samples were also obtained from a garden about 400 km from Kibera slum, with no surrounding industrial activities and irrigation done using clean tap water.
The vegetable samples (kales, amaranths, and spinach), were washed with tap water to remove the soil particles adhered to the surface of the vegetables then rinsed with distilled water. The water on the surface of the leaves was removed with blotting papers, samples were cut into pieces and dried in an oven at 100˚C until a constant weight was achieved after which their midribs were removed. The dried samples were ground, sieved through 2 mm pore size sieve, and then stored at room temperature. Arrowroots were pilled, crushed, and dried in the oven at 100˚C before being pulverized and stored in polythene zip-bags.
The procedure according to [
The chemicals and reagents were of analytical grade (99.99% purity) manufactured by Sigma Aldrich Company. These were ; manganese metal wire, magnesium metal strip, chromium metal strip, iron metal fillings, zinc metal granules, copper strips, aluminium wire, lead metal, 70% perchloric acid, 68% concentrated nitric (V) acid, 6% nitric (V) acid and 10% nitric (V) acid.
Standard solutions of elements (1000 mg/L) were prepared using metals (manganese metal wire, magnesium metal strip, chromium metal strip, iron metal fillings, zinc metal granules, copper strips, aluminium wire, lead metal) of analytical grade (99.9% pure) and concentrated acids [
The operating parameters for the AAS (Shimadzu AA-6300) equipment were set according to the manufacturer’s specifications. The Air-C2H2 flame was used to analyze all the metals. The detection limit was set at ≤0.01000 ppm, repeatability ≤ 2.00%, and stability ≤ 6.0% [
Data were analyzed using SPSS software version 21 for parameters as mean, standard deviation, one-way ANOVA (at 95% confidence level).
The mean levels (µg/g) of essential and non-essential elements in kales, amaranths, spinach, and arrowroots from gardens in Kibera slum are presented in
Sample (n = 3) | Gardens | Mn | Mg | Fe | Zn | Cu | Al |
---|---|---|---|---|---|---|---|
Arrowroot | Control | 148.57 ± 0.98a | 261.22 ± 0.44a | 809.33 ± 0.93a | 1.18 ± 0.03a | 2.79 ± 0.05a | |
U001 | 148.71 ± 0.41a | 274.44 ± 1.38b | 1114.50 ± 8.96b | 2.06 ± 0.01c | 4.16 ± 0.03e | ||
U002 | 193.40 ± 0.74b | 261.28 ± 0.33a | 1191.83 ± 3.37c | 1.36 ± 0.05a | 3.52 ± 0.02d | ||
U003 | 226.42 ± 2.99c | 275.47 ± 0.14b | 1273.67 ± 2.19f | 1.57 ± 0.03b | 3.52 ± 0.02d | ||
U004 | 189.73 ± 4.97b | 274.22 ± 1.18b | 1212.67 ± 2.35d | 5.68 ± 0.11e | 3.29 ± 0.03c | ||
U005 | 150.76 ± 0.64a | 282.86 ± 0.80c | 1233.00 ± 3.62e | 2.26 ± 0.12c | 3.17 ± 0.02b | ||
U006 | 185.74 ± 0.41b | 273.21 ± 0.83b | 1222.83 ± 4.85d | 2.63 ± 0.02d | 3.10 ± 0.04b | ||
P-Values | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 | ||
Amaranth | Control | 176.73 ± 2.29a | 282.54 ± 0.02b | 422.50 ± 3.33a | 1.07 ± 0.02a | 4.20 ± 0.06a | |
U001 | 171.04 ± 1.06a | 287.07 ± 0.20c | 722.50 ± 5.86f | 4.05 ± 0.05c | 5.39 ± 0.11d | ||
U002 | 234.61 ± 0.33c | 282.81 ± 0.40b | 687.17 ± 1.76e | 3.74 ± 0.04b | 6.48 ± 0.15f | ||
U003 | 293.62 ± 5.92e | 284.85 ± 0.10c | 604.50 ± 2.08e | 6.33 ± 0.07d | 6.01 ± 0.08e | ||
U004 | 198.75 ± 1.61b | 279.46 ± 1.33a | 621.83 ± 3.47d | 3.60 ± 0.07b | 4.52 ± 0.02b | ||
U005 | 250.40 ± 1.47d | 279.62 ± 0.30a | 788.50 ± 1.04g | 3.55 ± 0.06b | 5.38 ± 0.11d | ||
U006 | 174.23 ± 0.89a | 277.79 ± 0.36a | 512.17 ± 6.93b | 3.55 ± 0.06b | 4.85 ± 0.09c | ||
P-Values | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 | - | |
Spinach | Control | 116.24 ± 0.71a | 529.73 ± 0.18a | 517.33 ± 3.81a | 0.57 ± 0.04a | 5.25 ± 0.12a | |
U001 | 193.00 ± 6.76d | 532.03 ± 0.09c | 696.33 ± 2.80e | 4.28 ± 0.05d | 7.82 ± 0.09c | 1.09 ± 0.00a | |
U002 | 181.12 ± 1.90c | 532.89 ± 0.02d | 624.00 ± 4.48c | 4.48 ± 0.07e | 9.53 ± 0.02e | 1.06 ± 0.00a | |
U003 | 153.39 ± 0.16b | 532.96 ± 0.03d | 596.67 ± 2.89b | 4.74 ± 0.01f | 8.53 ± 0.17d | 2.00 ± 1.41a | |
U004 | 148.41 ± 0.97b | 532.28 ± 0.25c | 719.83 ± 2.24f | 4.96 ± 0.04g | 9.29 ± 0.10e | 1.22 ± 0.00a | |
U005 | 374.44 ± 1.55e | 531.06 ± 0.05b | 637.83 ± 1.92d | 3.98 ± 0.07c | 6.77 ± 0.03b | 1.63 ± 0.00a | |
U006 | 172.84 ± 0.98c | 531.21 ± 0.41b | 618.00 ± 3.75b | 1.18 ± 0.04b | 6.99 ± 0.10b | 2.29 ± 0.05a | |
P-Values | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 | 0.618 | |
Kales | Control | 74.74 ± 1.54a | 527.36 ± 0.41a | 268.05 ± 2.61a | 0.51 ± 0.01a | 2.44 ± 0.04a | |
U001 | 147.06 ± 2.44d | 529.00 ± 0.12b | 518.17 ± 3.28d | 5.41 ± 0.14f | 4.57 ± 0.06b | 1.16 ± 0.03a | |
U002 | 121.43 ± 1.64f | 531.26 ± 0.02c | 619.50 ± 0.87e | 2.22 ± 0.07e | 5.92 ± 0.12c | 1.07 ± 0.02a | |
U003 | 121.43 ± 1.64c | 531.26 ± 0.02d | 619.50 ± 0.87g | 2.22 ± 0.07b | 5.92 ± 0.12b | 1.23 ± 0.03b | |
U004 | 171.09 ± 3.31e | 530.68 ± 0.10c | ± 585.671.64f | 2.59 ± 0.04c | 4.13 ± 0.57b | 1.53 ± 0.02d | |
U005 | 141.92 ± 1.07d | 527.06 ± 0.12a | 362.67 ± 3.49c | 2.97 ± 0.07d | 3.02 ± 0.02a | 1.46 ± 0.04c | |
U006 | 91.04 ± 2.31b | 530.02 ± 0.22c | 350.74 ± 2.34b | 2.59 ± 0.04c | 2.81 ± 0.06a | 1.27 ± 0.06b | |
P-values | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 | |
[ | 500 - 15 20 - |
Mean values followed by the same small letter(s) within the same column do not differ significantly from one another (SNK-test, α = 0.05). Where n is the number of replicates and LOD is lower limit of detection.
Sample (n = 3) | Gardens | Cr (Mean ± SE) µg/g | Pb |
---|---|---|---|
Arrowroots | Control | 2.03 ± 0.02a | |
U001 | 2.45 ± 0.02b | 0.86 ± 011f | |
U002 | 2.73 ± 0.04c | 0.94 ± 0.32d | |
U003 | 3.72 ± 0.04f | 0.43 ± 0.05e | |
U004 | 3.05 ± 0.02d | 0.32 ± 0.02d | |
U005 | 3.36 ± 0.05e | 0.46 ± 0.01c | |
U006 | 2.63 ± 0.02 c | 0.65 ± 0.02e | |
P-value | <0.001 | <0.001 | |
Amaranthus | Control | 1.55 ± 0.02a | |
U001 | 3.72 ± 0.03f | 0.34 ± 0.07d | |
U002 | 4.32 ± 0.03g | 0.35 ± 0.02a | |
U003 | 3.25 ± 0.04e | 0.79 ± 0.02d | |
U004 | 2.99 ± 0.01d | 0.31 ± 0.01a | |
U005 | 2.09 ± 0.02b | 0.33 ± 0.08a | |
U006 | 2.56 ± 0.02c | 0.14 ± 0.01b | |
P-value | <0.001 | <0.001 | |
Spinach | Control | 1.15 ± 0.02a | |
U001 | 2.64 ± 0.03d | 0.02 ± 0.17c | |
U002 | 2.44 ± 0.01c | 0.32 ± 0.16e | |
U003 | 2.65 ± 0.06d | 0.44 ± 0.14c | |
U004 | 2.38 ± 0.04c | 0.21 ± 0.18f | |
U005 | 4.07 ± 0.01e | 0.62 ± 0.32d | |
U006 | 1.80 ± 0.05b | 0.45 ± 0.07c | |
P-value | <0.001 | <0.001 | |
Kales | Control | 2.35 ± 0.06a | |
U001 | 2.58 ± 0.02a | 0.75 ± 0.01a | |
U002 | 3.35 ± 0.04c | 0.84 ± 0.02b | |
U003 | 2.57 ± 0.03a | 0.63 ± 0.01a | |
U004 | 2.95 ± 0.01b | 0.44 ± 0.00a | |
U005 | 3.16 ± 0.03c | 0.86 ± 0.03c | |
U006 | 3.01 ± 0.03b | 0.91 ± 0.06d | |
P-value | <0.001 | <0.001 | |
Permissible levels of [ | 1 | 0.43 |
Mean values followed by the same small letter(s) within the same column do not differ significantly from one another (SNK-test, α = 0.05). n is a number of replicates. LOD is Lower limits of detection.
being below [
As shown in
The DIM values calculated for adults are presented in
For non-essential elements, the ranges were Cr 0.02 - 0.09 and Pb 0.01 - 0.02 being below the standards of [
FOOD CROP [ | DIM VALUES (mg/day) in food crops | |||||||
---|---|---|---|---|---|---|---|---|
ESSENTIAL ELEMENTS | NON ESSENTIAL ELEMENTS | |||||||
Mn (2.3) | Mg | Fe (8.0) | Zn (11) | Cu (0.9) | Al | Cr (1.5) | Pb (0.5) | |
Arrowroots | 3.85 | 5.89 | 24.95 | 0.05 | 0.07 | - | 0.06 | 0.02 |
Amaranths | 6.11 | 6.11 | 13.5 | 0.08 | 0.11 | - | 0.06 | 0.01 |
Spinach | 11.53 | 11.53 | 13.66 | 0.07 | 0.17 | 0.03 | 0.05 | 0.01 |
Kales | 11.48 | 11.48 | 10.11 | 0.07 | 0.09 | 0.03 | 0.06 | 0.01 |
index for Cr and Pb were generally lower than the permissible levels of [
The THQ values from the levels of essential and non-essential elements are presented in
The range of the values is Mn (1.65 - 8.27), Fe (1.18 - 5.63) Cu (0.003 - 0.007). Zn (0.001 - 0.006), Mg (0.0 1 - 0.01), and decreased in the same order (Mn being highest). The results point out to health risks such as irritability, stomach upsets, cancer and dibetes that would be associated with consumption of the food crops with high levels of Mn and Fe whose THQ was greater than unity [
The results on the levels of non-essential elements in food crops grown in Kibera slum were used to calculate the THQ values and result are presented (
The calculated results for ILCR for Pb in adults are given in
FOOD CROP [ | THQ Values in food crops | ||||||
---|---|---|---|---|---|---|---|
ESSENTIAL ELEMENTS | NON ESSENTIAL ELEMENTS | ||||||
Mn > 1 | Mg | Fe > 1 | Zn < 1 | Cu < 1 | Cr < 1 | Pb < 1 | |
Arrowroots | 3.923 | 0.008 | 5.084 | 0.002 | 0.023 | 0.285 | 0.084 |
Amaranths | 4.697 | 0.008 | 2.751 | 0.039 | 0.039 | 0.287 | 0.034 |
Spinach | 4.228 | 0.015 | 2.784 | 0.061 | 0.061 | 0.238 | 0.203 |
Kales | 3.067 | 0.015 | 2.060 | 0.032 | 0.032 | 0.285 | 0.340 |
Vegetable | U001 | U002 | U003 | U004 | U005 | U006 | Total |
---|---|---|---|---|---|---|---|
Arrowroots | 4 | 17 | 2 | 2 | 2 | 2 | 29 |
Kales | 4 | 4 | 2 | 2 | 4 | 4 | 20 |
Spinach | 2 | 2 | 2 | 2 | 2 | 2 | 12 |
Amaranths | 2 | 4 | 2 | 2 | 2 | 0 | 12 |
Grand total | 12 | 27 | 8 | 8 | 10 | 8 | 73 |
This results showed that ILCR for lead alone a total of 73 residents of the 0.17 M which translates to 0.043% likely to develop cancer in a lifetime due to the long-term exposure to non-essential elements. In Kenya cancer is the third leading cause of morbidity (7% deaths per year), after infectious and cardiovascular diseases. It is estimated that 39,000 new cases of cancer are reported every year with more than 27,000 deaths per year with the leading cancer being prostrate (men) and breast cancer (female) [
Amaranths, spinach, arrow roots, and kales grown in Kibera slum through peri-urban agriculture contained high levels of essential and non-essential elements and consequently alarming DIM and THQ health risk indices for Mn and Fe elements. Incremental lifetime cancer risk index (ILCR) showed that from lead alone almost 73 (0.043%) residents are likely to develop cancer in Kibera slum.
A sensitization strategy is called for use of safe water for peri-urban farming in this slum.
The Department of Chemistry, Kenyatta University, and Kenya Institute of Research Development (KIRD).
The authors declare no conflicts of interest regarding the publication of this paper.
George, N., Mildred, N. and Hudson, N. (2019) Health Risk Assessment on Selected Essential and Non-Essential Elements in Food Crops Grown in Kibera Slum, Nairobi-Kenya. Food and Nutrition Sciences, 10, 635-647. https://doi.org/10.4236/fns.2019.106047