This document summarizes a study that analyzed heavy metal concentrations in vegetables sold in Maun, Botswana. The study found that: 1) Vegetables from street vendors contained higher levels of essential metals like iron and zinc, but lower levels of toxic metals like lead and cadmium compared to vegetables from supermarkets. 2) Some vegetables, especially leafy greens, from supermarkets contained toxic metal levels above international safety standards. 3) While many vegetables provided beneficial essential metals, regular monitoring of heavy metal pollution is needed and consumption amounts should be limited to prevent health risks from toxic metal accumulation.

1. Determination of selected heavy
metals in vegetables sold in the
market of Maun
Keagile Bati
Supervised by:
Prof. W Masamba
Ms O Mogobe

2. INTRODUCTION
• Heavy metals are high density chemical
elements with high potential of
environmental toxicity (Singh, 2006).
• Some are essential at low concentrations
but toxic at higher concentrations, e.g Fe,
Zn, Mn (WHO, 2006).
• Some are highly toxic even at low
concentrations eg Pb, Cd, Cr, As.
• In Nigeria 5,451 people suffered
from lead poisoning, 400 kids
died in Nigeria (U.S. EPA, 2010).
• A study conducted on a sample of
228 children in Gaborone has
shown that 30% of children have
lead poisoning (Mbogwe, 2007)
2

3. Problem statement
• Vegetables are a very important
component of the human diet.
• They provide vitamins, fibre,
carbohydrates (Kumar, 2007).
• Contamination of vegetables with
heavy metals pose threat to
human life. Vegetables contribute
70% cadmium intake (Rivera –
becelli, 2002).
• Cancer, cardiovascular diseases,
nervous system disorders, bone
disorders (Guerra, 2012)
• Heavy metal contamination of
vegetables:
• Anthropogenic and natural acts
• Research studies resulted in
Maximum permissible limits in
food set by FAO/WHO, FDA,
US. EPA
• The exposure to and health risk of
these contaminants at HIGH
CONCENTRATIONS is still a
big problem in many countries.
3

4. Research objectives
General objective
To determine the concentrations of heavy metals in different vegetables sold in
the market of Maun.
Specific objectives
•To determine the concentrations of 5 essential heavy metals (Cu, Mn, Mo, Zn
and Fe) in vegetables.
•To determine the concentrations of 5 toxic heavy metals (Pb, As, Cd, Cr ) in
vegetables.
•To identify the source of the vegetables in each selected market site.
•To compare the concentrations of the selected heavy metals in vegetables with
the international standards.
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5. Methodology
Study Site
• Maun shopping centre
Sampling technique
• Purposive sampling for supermarkets
and street vendors
Sample size
• 9 market sites:4 supermarkets and 5
street vendors.
• 5 types of vegetables were bought
from each market site in triplicate.
• rape, tomatoes, onions, cabbage,
potatoes
Sample preparation and analysis
• Samples cleaned with DDI, cut and
dried at 60 ‘C for 18 hours.
• Ground and digested with aqua regia
(EPA, 2007)
• Filtered and analyzed on ICP – OES
5

6. Data analysis
• Mean values and standard error of triplicates was
calculated using Microsoft excel.
• Mean concentrations of metals in vegetables were
compared to the World Health Organisation (WHO)
and Food and Drug Administration (FDA).

7. RESULTS
• Source of vegetables
7
0
10
20
30
40
50
60
70
80
90
100
street vendors supermarkets
percentage(%)
market site
import
locally

8. Essential metals
Iron
• RDA; 8 – 18 mg/day (FAO/WHO,
2001)
8
0
100
200
300
400
500
600
700
800
1 2 3 4
Iron[mg/Kg]
Supermarkets
Rape
tomatoes
onions
cabbage
potatoes
0
20
40
60
80
100
120
1 2 3 4 5
Iron[mg/Kg]
Street vendors
Rape
Tomatoes
onion

9. Essential elements
Zinc concentrations
• RDA; 8 – 11 mg/day (FAO/WHO,
2001)
9
0
5
10
15
20
25
30
35
40
45
50
1 2 3 4 5
Zinc[mg/Kg]
Street vendors
Rape
Tomatoes
onion
0
200
400
600
800
1000
1200
1400
1600
1 2 3 4
Zinc[mg/Kg]
Supermarkets
rape
cabbage
tomatoes
onion
potatoes

10. Toxic metals
Chromium
• MRL; 2300 µg/Kg (FAO/WHO, 2003)
10
0
100
200
300
400
500
600
700
1 2 3 4 5
Chromium[ug/Kg]
Street vendors
rape
tomatoes
onion
0
5
10
15
20
25
30
35
1 2 3 4
Chromium[ug/Kg]
supermarkets
rape
tomatoes
onions
cabbage
potatoes

11. Toxic metals
Pb
• MRL; 2000µg/Kg (FAO/WHO)
11
0
500
1000
1500
2000
2500
3000
3500
1 2 3 4
Lead[ug/Kg]
Supermarkets
rape
tomatoes
cabbage
onion
potatoes
0
200
400
600
800
1000
1200
1 2 3 4 5
Lead[ug/Kg]
Street vendors
rape
tomatoes
onion

12. Discussion
Essential metals
Zinc: 17 – 44 mg/Kg (RDA; 8 – 11 mg/day
WHO). Beneficial for children with
stunted growth, a problem that exist in
Botswana (UNICEF, 2009).
Iron: 64 – 718 (RDA; 8 – 18 mg/day
FDA,2001)
• 100g portion provide more than 100% -
good for blood system, prevent anemia
(Arora et al. 2008)
Toxic metals
Arsenic: 100 – 820 µg/Kg (100 µg/Kg WHO)
• High concentrations – cardiovascular and
kidney diseases (Ramirez-Andreotta et al.
2013)
Cadmium:
• 180 – 718 µg/Kg (20 µg/Kg WHO) High
concentrations – bone decalcification and
renal damage (Umar et al. 2014).
Chromium
• 0 – 666 µg/Kg (MPL; 2300 µg/Kg WHO)
• Safe for human health
Lead
• 18 – 2900 µg/Kg (2000 µg/Kg WHO)
• Some vegetables above the limit, unsafe
for human health.
• High concentrations associated with
mental retardation and cancer,
hypertension (Guerra et.al, 2012)
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13. conclusion
• Vegetables from street vendors; high essentials and low toxic
metals.
• Good amount of essential metals, suitable for human health.
• Most of vegetables from supermarkets had high concentrations
of toxic metals above permissible limits.
• Toxic metal concentration within WHO MRL for some
vegetables safe for consumption.
• Leaf vegetables from both street vendors and supermarkets
accumulated high concentrations of toxic metals.
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14. Recommendations
• Since this findings are preliminary results,
more research need to be done with more samples as
a confirmatory.
• Frequent monitoring and health risk assessments for
heavy metal pollution need to be done.
• Small amounts of vegetables should be consumed to
prevent excessive bio-accumulation of heavy metals.
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15. CAUTION!!!
15
BEWARE OF HEAVY METAL
CONTAMINATED VEGETABLES!!!!!!
THANK YOU!!!!!