LEVELS OF CADMIUM, CHROMIUM AND LEAD IN Clarias gariepinus (CAT FISH) INHABITING SOME STREAMS OF BLANTYRE CITY- MALAWIDixon Gift Mlelemba, Chemistry Dpt, Chancellor College, P.O. Box 280, Zomba, MalawiEmail: dix.el@hotmail.com

ABSTRACT

Cadmium, Chromium and lead levels in Clarias gariepinus, sediment and pore-water from

Nasolo, Naperi Limbe and Mudi streams were determined. Samples were digested in nitric acid

and absorbance read using atomic absorption spectroscopy. Cadmium concentrations ranged

from below detection limit to 0.061 mg l-1 in pore-water, from 0.102 to 0.945 mg kg-1 in Clarias

gariepinus and from below detection limit to 0.2977 mg kg-1 in sediment. Chromium levels

ranged from below detection limit to 0.258 mg l-1 in pore water, 0.017 to 7.576 mg kg-1 in

sediment and from below detection limit to 0.021 mg kg -1 in Clarias gariepinus. Lead values

ranged from no detection to 0.116 mg l-1 in pore water, 0.089 to 2.580 mg kg-1 in sediment and

from 0.096 to 0.377mg kg-1 in Clarias gariepinus. Based on Pearson’s correlation, pH of pore

water was strongly and negatively correlated to cadmium (-0.848; p = 0.007) and chromium

concentration (-0.971; p = 0.029) in Clarias gariepinus indicating increased metal

bioavailability at low pH. There was also relatively higher levels of cadmium in Clarias

gariepinus compared to pore water with p<0.05. pH values for sediment were lower than pH

values of pore water in all streams under study. There was a wider range of bioconcentration

factor (BCF) and biota to sediment accumulation factor (BSAF) in the streams studied. BCF for

cadmium was found to be up to 16.67 in Nasolo stream while BSAF was up to 34.33 in Naperi

stream. BCF for chromium of up to 0.021 in Mudi stream and BSAF of up to 0.038 in Naperi

i

stream have been found. BCF and BSAF values indicate high levels of cadmium and low levels

of chromium in Clarias gariepinus. The research has revealed that levels of heavy metals in

Clarias gariepinus are lower than maximum limit levels of World Health organization. In

addition, consumption of Clarias gariepinus (catfish) does not pose health hazard with regard

studied heavy metal contamination.

ii

TABLE OF CONTENTS

ABSTRACT....................................................................................................................................... i

TABLE OF CONTENTS..................................................................................................................... iii

TOPIC 1...................................................................................................................................... 1INTRODUCTION, LITERATURE REVIEW AND OBJECTIVES...............................................................1

1.2 Introduction and literature review..............................................................................11.2 Objectives....................................................................................................................3

1.2.1 General objective.................................................................................................31.2.2 Specific objectives................................................................................................3

TIPIC 2........................................................................................................................................ 4METHODS AND MATERIALS...........................................................................................................4

2.1 Overview......................................................................................................................... 42.2 Sampling and sample preparation...................................................................................4

2.2.1 Determination of heavy metals in Clarias gariepinus...........................................42.2.2 Determination of heavy metals in pore-water samples.......................................52.2.3 Determination of heavy metals in sediment........................................................52.2.4 Determination of pH in pore-water......................................................................52.2.5 Determination of pH in sediment.........................................................................6

2.2 Preparation of standard and working solutions..............................................................62.3.1 Cadmium..............................................................................................................62.3.2 Chromium.............................................................................................................62.3.3 Lead......................................................................................................................6

2.4 Data analysis................................................................................................................... 7

TOPIC 3...................................................................................................................................... 8RESULTS AND DISCUSSION............................................................................................................ 8

3.1 Cadmium..................................................................................................................... 83.2 Chromium....................................................................................................................93.3 Lead........................................................................................................................... 10

TOPIC 4.................................................................................................................................... 11CONCLUSION AND WAYFORWARD..............................................................................................11

REFERENCE.............................................................................................................................. 12

Appendices.............................................................................................................................. 15

iii

TOPIC 1

INTRODUCTION, LITERATURE REVIEW AND OBJECTIVES

1.2 Introduction and literature review

Heavy metal is a general term applied to a metal or metalloid, which has atomic density

greater than 4g/cm3 (at least 5 times or more than water). Toxic heavy metals are

persistent environmental contaminants because they can not be degraded or destroyed. To

a small extent, they enter the body system through food, air and water. They bio-

accumulate over a period of time because they cannot be metabolized (Lenntech, 2004).

Heavy metal toxicity can lead to damaged or reduced mental and central nervous

functioning, damage of vital internal organs and lowering of energy levels in the body.

There are more than 20 heavy metals but this research looked at cadmium, lead and

chromium. These metals are highly toxic such that they can cause damaging effects even

at low concentrations (Tuberose, 2007). There is great concern of trace metals in foods,

which has prompted several bodies such as World Health Organization [WHO] to

establish maximum allowable concentrations of these metals in food (WHO, 1984).

Problems of heavy metal contamination especially mercury toxicity from fish

consumption has been reported in other parts of the world (Edorh, 2007; Rose et al, 1999;

Piotrowski and Inkship, 1981). Trace metal studies in Nigerian urban fish indicated high

levels of lead and cadmium due to accumulation of these metals from contaminated food

and polluted environment, which poses great health hazard to consumers (Abulude et al,

2007). Other studies investigated bioavailability of heavy metals in tuna fish from the

Red Sea and Persian Gulf. The results from these studies were compared with

international literature values (Waqar, 2001)

Despite comparatively low industrial activities in Blantyre city, the streams are becoming

exposed to unwanted ecological effects of heavy metals due to uncontrolled disposal or

poor management of industrial effluent. Other sources of water pollution are surface

runoffs from domestic and agricultural activities coupled with vehicular emissions into

1

drainage systems. These drainage systems are connected to the city’s streams without

being subjected to pretreatment. Studies have shown that some streams in Blantyre city

are polluted with metal pollutants such as lead, chromium, cadmium and nickel. These

studies revealed further that waste water treatment plants in the city do not significantly

reduce heavy metals in waste water (Sajidu et al, 2007). Water from these treatment

plants is channeled to various streams in the city. Studies on soil samples near major

roads in Blantyre city have shown relatively high concentrations of heavy metals

(Masamba and Chimbalanga, 2001; Lakudzala et al, 1999; Kadewa et al, 2001).

Consequently, these metals are washed into city streams, which lead to more pollution.

Studies from the same area have shown that earthworms can accumulate heavy metals in

their body tissues (Kaonga, 2007).

Heavy metal pollution is a reality in Africa but many nations have not yet conducted

systematic studies to estimate the impact of the phenomenon; detailed surveys on

accumulation of these pollutants in aquatic ecosystems and evaluations of the impact of

heavy metals on the environment and public health is also lacking (Edorh, 2007). A lot of

data about heavy metal pollution has been accumulated on soil and water. Therefore this

research was carried out in view of scarcity of information on bioavailability of heavy

metals in Clarias gariepinus, commonly known as catfish and to find out the effect of

heavy metal pollution on Clarias gariepinus. Marine organisms such as fish accumulate

contaminants from aquatic environment and therefore fish have been used extensively in

monitoring pollution of aquatic environment (Henry et al, 2004).

Levels of cadmium, chromium and lead were determined in sediment and pore-water in

relation to levels of these heavy metals in Clarias gariepinus (cat fish) because Clarias

gariepinus spends most of its time in sediment and pore-water. pH levels were also

determined because metal ions have different solubility at different pH levels and this

affect concentrations of heavy metals. Biomagnification effects such as bioconcentration

factor (BCF) and biota to sediment accumulation factor (BSAF) have been used to relate

pollutant residues in Clarias gariepinus to the pollutant concentration in pore-water. BCF

is the ratio of chemical concentration in an organism to that in surrounding water.

2

Bioconcentration occurs through uptake and retention of a substance from water only,

through gill membranes or other external body surfaces while BSAF occurs through

sediment-mediated exposures and is calculated by concentrations of chemicals in an

organism divided by the concentrations of the same chemicals in sediment.

1.2 Objectives

1.2.1 General objectiveThe research determined levels of cadmium, chromium and lead in Clarias gariepinus in

relation to levels in sediment and pore-water

1.2.2 Specific objectivesThis research was designed to:

(i) Find levels of cadmium, lead and chromium in pore-water, sediment and

Clarias gariepinus.

(ii) Compare concentrations of lead, cadmium and chromium of pore-water to that

of sediment and Clarias gariepinus.

(iii) Compare pH values of pore-water and sediments and find their relationship to

heavy metal concentrations in Clarias gariepinus, pore-water and sediments.

3

TOPIC 2

METHODS AND MATERIALS

2.1 OverviewSamples were collected from Mudi, Nasolo, Naperi and Limbe streams in triplicates.

Two sampling points were identified for each stream to represent upper and down stream.

Fish, water and sediment samples were digested in nitric acid and concentration of heavy

metals was determined using atomic absorption spectrophotometer method (AOAC, 1990

and APHA, 1985). All chemicals and reagents used in this procedure were of analytical

grade (AR). Buck Scientific Atomic Absorption Spectrophotometer Model 200A was

used in this research. Detection limits for each metal on the instrument are: cadmium:

0.005 mg.L-1, chromium: 0.005 mg.L-1 and lead: 0.1000mg.L-1.

2.2 Sampling and sample preparation

2.2.1 Determination of heavy metals in Clarias gariepinusClarias gariepinus samples were collected and packed in plastic bags, which were kept in

cooler box. Samples were kept frozen pending analysis. Samples were dried at 105 oC

and blended. 0.5g of the sample was ashed at 550 oC overnight in a muffle furnace.

Ashed samples were then transferred quantitatively to 100ml glass (Pyrex) beaker.

Crucibles used for ashing were washed with 25ml of 20% nitric acid (HNO3) solution as

part of qualitative transferring. The washouts were added to the ashed samples in a

beaker and then warmed in fume hood just up to boiling. The solution was left to cool

and then filtered using gravity into a 50ml volumetric flask and made to the mark with

distilled water (AOAC, 1990). Samples were run on Atomic Absorption

Spectrophotometer.

4

Figure1: Sample collecting at Mudi stream (MDI)

2.2.2 Determination of heavy metals in pore-water samples Pore-water samples were collected in 1-litre plastic bottles. Pore-water was collected

from the points where fish was found. 1ml concentrated nitric acid was added to each

sample. Samples were digested in nitric acid and filtered. The filtrate was diluted to the

mark in 100ml volumetric flask with distilled water (APHA, 1985). Heavy metal

concentrations were determined using Buck Scientific AAS.

2.2.3 Determination of heavy metals in sedimentSediment samples were collected in plastic bags. Sediment samples were collected from

points where fish was found. Sediment samples were air dried and ground using Ritsch

electric grinder (model: RM 100). Samples were then sieved in 2mm sieve. 10ml of

concentrated nitric acid was added to 2g of the sample and refluxed in a 100ml beaker for

45 minutes, and then evaporated to dryness. 5ml of 3:1 HCl and HNO3 (aqua regia) was

added to dried sample and then filtered (Bamgbose, 2000 cited in Kaonga, 2007). Buck

Scientific AAS was used to determine concentrations of heavy metals.

2.2.4 Determination of pH in pore-waterpH of water samples was measured on the same day of sampling using Metrohm pH

meter model 827, which was calibrated using buffers of pH4 and 7.

5

2.2.5 Determination of pH in sediment40g of ground and sieved sample was stirred for 30 seconds in every 3 minutes for time

lapse of 15 minutes in 40ml of distilled water to get suspension of sediment in water. The

mixture was allowed to settle for 5 minutes. Then the pH of the supernatant was

measured after calibrating the pH meter using buffers of pH 4 and 7.

2.2 Preparation of standard and working solutions

2.3.1 Cadmium1.000 g of cadmium metal was dissolved in 20 ml of 1+1 HCl and then diluted to 1000

ml to make 1000 mg l-1 Cd stock solution. An intermediate stock solution of 100 mg. L -1

Cd was made from the stock solution and a series of working standards of the following

concentrations were prepared: 0.0, 0.5, 1.0, 2.0, 3.0, 5.0, 7.0 and 10.0 mg l-1 Cd. The

absorbance was determined on AAS and wavelength set at 228.9 nm.

2.3.2 Chromium2.828 g of anhydrous potassium dichromate (K2Cr2O7) was dissolved in 200 ml distilled

water and 1.5 ml concentrated HNO3 was added and then diluted to 1000 ml with

distilled water to make 1000 mg l-1 Cr. An intermediate tock solution of 100 mg l -1 Cr

was made from the stock solution and a series of working standards of the following

concentrations were prepared: 0.0, 0.5, 1.0, 2.0, 3.0, 5.0, 7.0 and 10.0 mg l -1 Cr. The

absorbance was determined on AAS and wavelength set at 357.9 nm.

2.3.3 Lead1.598 g of lead nitrate (Pb(NO3)2) was dissolved in 200 ml distilled water and 1.5 ml

concentrated HNO3 was added and then diluted to 1000 ml to make 1 000 mg l -1 Pb. An

intermediate stock solution of 100 mg l-1 Cr was made from the stock solution and a series

of working standards of the following concentrations were prepared: 0.0, 0.5, 1.0, 2.0,

6

3.0, 5.0, 7.0 and 10.0 mg l-1 Cr. The absorbance was determined on AAS and wavelength

set at 283.7 nm (APHA, 1985).

2.4 Data analysis

The Statistical Package for Social Scientists (SPSS) version 11.0 was used for

correlations. Pearson correlations were used because levels of heavy metals in sediments

and pore-water were assumed to be linearly related to the levels in Clarias gariepinus.

Microsoft excel was used for standard deviation of the mean, t-test, biota to sediment

accumulation factor (BSAF) and Bio-accumulation factor (BCF). Graphs were plotted

using Microsoft Excel. Independent sample t-test was used because of an assumption that

sampling points are independent of each other.

7

TOPIC 3

RESULTS AND DISCUSSION

3.1 Cadmium

The range of cadmium concentration in pore-water ranged from no detection to 0.061 mg

l-1 and from 0.102 mg kg-1 to 0.945 mg kg-1 in Clarias gariepinus. Maximum allowable

concentration of lead in fish is 0.0002 mg kg-1 (USEPA, 1987) and the results indicate

exceeding levels. Based on Pearson’s correlation, there was significant negative

correlation between the pH of pore-water and cadmium concentration in biota (-0.848; p

= 0.007). The results indicate increased metal bioavailability in Clarias gariepinus at low

pH. This means that more of the metal will be in solution form at low pH resulting in

increased metal uptake by Clarias gariepinus. Clarias gariepinus indicated significantly

higher levels of cadmium than pore-water (p<0.05). This explains bioaccumulation of

cadmium in Clarias gariepinus over a long period as shown by high ratios of BCF and

BSAF. BCF for cadmium was found to be up to 16.67 in Nasolo stream while BSAF was

up to 34.33 in Naperi stream.

Cadmium levels

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Nasolo (BNC) Nasolo (SRN) Naperi(Rainbow )

Naperi (MoiRd)

Limbe(Mpingw e)

Limbe (HighWay)

Mudi (MDI) Mudi (SRN)

Sampling point

Con

cent

ratio

n (m

g/L

or m

g/K

g)

Pore-waterSedimentClarias gariepinus

Figure 2

8

3.2 Chromium

Concentration of chromium in pore-water ranged from no detection to 0.258 mg l -1,

0.0167 mg kg-1 to 7.6367 mg l-1 in sediment and no detection to 0.021 mg k -1 in Clarias

gariepinus. Levels of chromium in Clarias gariepinus were far below maximum

allowable limit of 0.008 mg kg-1 (USEPA, 1987). There was significant negative

correlation between amount of chromium in pore-water and pH of pore-water (-0.971; p

= 0.029). Low pH of pore water result in increased amount of the metal in pore water.

This phenomenon explains why there was significant correlation between the level of

chromium in Clarias gariepinus and pH of pore water (-0.935; p = 0.020). At low pH,

more of the metal will be in solution form resulting in increased metal bioavailability in

Clarias gariepinus at low pH. Level of chromium in sediment was significantly higher

than the level in pore-water because p<0.05. Levels of chromium were high in sediments

and little traces in Clarias gariepinus. This could suggest that more of chromium was in

precipitated and settled in sediments.

Chromium levels

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

6.5

7

7.5

8

Nasolo(BNC)

Nasolo(SRN)

Naperi(Rainbow)

Naperi (MoiRd)

Limbe(Mpingwe)

Limbe (HighWay)

Mudi (MDI) Mudi (SRN)

Stream

Con

entr

atio

n (m

g/L

or m

g/K

g)

Pore-waterSedimentClarias gariepinus

Figure 3

9

3.3 LeadLead concentrations ranged from below detection limit to 0.1157 mg l -1 in pore-water,

0.089 mg l-1 to 2.580 mg kg-1 in sediment and 0.096 mg kg-1 to 0.3767 mg kg-1 in Clarias

gariepinus. Lead concentration in Clarias gariepinus was less than WHO limit of 0.004

mg kg-1 (USEPA, 1987). The results showed that sediment concentration was

significantly higher than pore-water concentration (p<0.05). There was a significant

correlation between levels of lead in sediment and pH of sediment (-0.856, p = 0.007).

This means that lead precipitated more at low pH and become part of solid in the

sediment. This agrees with what other studies have found that reduced sorption efficiency

of lead ion removal with a decrease in pH could be attributed to the presence of H+ ions

in the mixture, which compete with lead ions for the binding sites (Mataka et al, 2007).

Lead levels

0

0.5

1

1.5

2

2.5

3

Nasolo (BNC) Nasolo (SRN) Naperi(Rainbow)

Naperi (Moi Rd) Limbe(Mpingwe)

Limbe (HighWay)

Mudi (MDI) Mudi (SRN)

Stream

Con

cent

ratio

n (m

g/L

or M

g/K

g)

Pore-waterSedimentClarias gariepinus

Figure 4

10

TOPIC 4

CONCLUSION AND WAYFORWARD

The research generally found out that concentrations of heavy metals in Clarias

gariepinus are above allowable limits set by United State Environmental Protection

Agency (USEPA) and have been adopted by many countries. Generally, cadmium

showed the following trend in concentrations: Clarias gariepinus >sediment>pore-water,

while chromium showed a different trend: sediment>pore-water> Clarias gariepinus and

for lead: sediment> Clarias gariepinus >pore-water. There is no clear pattern of heavy

metal accumulation in parameters studied. pH levels of pore-water were found to be

higher than pH levels of sediments in all streams under study. The research therefore has

generated data that can be used for assessment of effects of heavy metal pollution on

Clarias gariepinus.

However, this study did not look into contribution of organic matter and wet season

samples. Only three toxic metals were studied and there is a gap that should be filled in

by future researchers. Frakas argued that levels of heavy metals in water bodies and fish

are a result of uptake and release processes with characteristic kinetics for elements in

their biological half life time, which are also influenced by the age of fish, feeding habits

and by season (Frakas et al, 2000). It is therefore important to look at other types of fish

and different age groups or other living organisms which have not yet been studied and

compare the findings with data that is already available. There is also need to carry out

further studies at microscopic level to determine variations in heavy metal accumulation

and distribution in different organs of Clarias gariepinus.

11

REFERENCE

Abulude, F. O., Obidiran, G. O., Elemide, O. A., and Abidakun, B., (2007). “Trace

metals distribution in Nigerian urban fishes”. Electronic Journal of Environment,

Agriculture and Food Chemistry, Vol. 6, (11), December Issue: 2512-2516. Available

online at <http://www.ejeafche.uvigo.com>

American Public Health Association, American Water Works Association and Water

pollution Control Federation, 1985. Standard Methods of examination of

Water/wastewater, 16th ed., APHA, AWWA and WPCF, New York: 150-152.

Association of Official Analytical Chemists, AOAC, (1990). Official methods of

analysis, 15th Ed. Washington DC.

Becker, E. W., (1983). Handbook of microalgal Mass Culture.

Edorh, P., (2007). “Heavy metal action”. TWAS newsletter, volume 19: 2. Available

online at <http://www.ictp.trieste.it/~twas/pdf

Farkas, A., Salanki, J and Varanka, I., (2000). “Heavy metal concentrations in fish of lake

Balaton”. Lakes and Reservoirs: Research and Management 2000: 271 – 279.

Förstner, U. and Prosi, (1979). Heavy metal pollution in freshwater ecosystems.

Biological Aspects of Freshwater Pollution (De. O. Ravera). Pergamon Press, New

York: 129-161.

Holum, J. R., (1983). Elements of general and biological chemistry, 6th Ed., John Wiley

and sons, New York: 324-326.

Kaonga,C.C, (2007). Levels of selected heavy metals and related physoco-chemical

parameters of algae, earthworms, soil and water in Blantyre city, Malawi: 42-57.

12

Khrishnakumar, P. K., (1994). “Effects of environmental contaminants on the health of

mytilus edulus”. Marine ecology series, number 106: 249-261.

Lenntech Water Treatment and Air Purification, (2004). “water treatment”. Lenntech,

Rotterdamseweg, Netherlands.

Masamba, W. R. L., Chimbalanga, R.M., (2001). “Heavy metal pollution in the city of

Blantyre, Malawi: lead, zinc and cadmium”. Proceedings of the first Chancellor

College Research Dissemination Conference. University of Malawi, Chancellor

College, Zomba: 315-332.

Mataka L.M., Masamba W.R.L., Henry E.M.T, and Sajidu S.M.I., (2007). Cadmium

removal from aqueous solutions using Moringa stenopetala and Moringa oleifera seed

powders:11

Ogwuegbu, M. O. and Ijioma, M. A., (2003). “Effects of certain heavy metals on the

population due to mineral exploitation”. Proceedings of International Conference on

Scientific and Environmental Issues In the Population, Environment and Sustainable

Development in Nigeria, University of Ado, Ekiti State, Nigeria: 8-10.

Piotrowski, J. K., and Inkship, M. J., (1985). “Review of Health Effects of

Methylmercury”. Journal of Applied Toxicology, Volume 5: 113-133.

Rose, J., Hutcheson, M. S., West, C. R., and Pancorbo, O., (1999). “Fish Mercury

Distribution in Massachusetts, USA Lakes”. Environmental Toxicology and

Chemistry, Vol. 18 (7): 1370-1379.

Sajidu, S.M.I., Masamba, W. R. L., Henry, E. M. T., Kuyeli, S. M., (2007). “Water

quality assessment in streams and waste water treatment plants of Blantyre, Malawi”.

13

Journal of Physics and Chemistry of the Earth, 07: 045. Available online at

<http://www.sciencedirect.com>

Tuberose, (2007). “Information for transformation” Available online at

<http://www.tuberose.com/Heavy_Metal_Toxicity.html>

World Health Organization (W.H.O.), (1984). “Guide lines for drinking water quality.”

Health criteria and other supporting information, General. Vol.

14

AppendicesAppendix 1: Correlation Table

pHpore-water

pHsediment

Cadmiumsediment

CadmiumPore-water

CadmiumClarias gariepinus(fish)

Leadsediment

LeadPore-water

LeadClarias gariepinus(fish)

Chromiumsediment

ChromiumPore-water

ChromiumClarias gariepinus(fish)

pHpore-water P Corr 1 -0.2872 -0.34014 -0.45596 -0.84819 -0.02608 0.035834 0.072296 -0.32777 -0.93477 -0.97051

Signf , 0.490372 0.50947 0.303829 0.007781 0.951129 0.946272 0.864917 0.428024 0.019802 0.02949n 8 8 6 7 8 8 6 8 8 5 4

pHsediment P Corr -0.2872 1 -0.54939 0.716816 0.076133 -0.85538 0.486315 -0.18314 -0.40601 -0.21539 0.015536

Signf 0.490372 , 0.258825 0.069879 0.8578 0.006765 0.328035 0.664222 0.318259 0.72789 0.984464n 8 8 6 7 8 8 6 8 8 5 4

Cadmiumsediment P Corr -0.34014 -0.54939 1 -0.5737 0.465272 0.614895 0.619209 0.179443 0.938908 0.633387 0.438555

Signf 0.50947 0.258825 , 0.311865 0.352452 0.193903 0.380791 0.733725 0.005484 0.563329 0.710981n 6 6 6 5 6 6 4 6 6 3 3

CadmiumPore-water P Corr -0.45596 0.716816 -0.5737 1 0.044218 -0.48858 -0.01586 -0.03016 -0.33586 0.305405 0.678704

Signf 0.303829 0.069879 0.311865 , 0.925006 0.265909 0.979812 0.948814 0.461438 0.617279 0.525084n 7 7 5 7 7 7 5 7 7 5 3

Cadmium fish P Corr -0.84819 0.076133 0.465272 0.044218 1 0.070267 0.052046 0.035697 0.484524 0.904301 0.575223Signf 0.007781 0.8578 0.352452 0.925006 , 0.868682 0.922002 0.933125 0.223689 0.035024 0.424777n 8 8 6 7 8 8 6 8 8 5 4

Leadsediment P Corr -0.02608 -0.85538 0.614895 -0.48858 0.070267 1 -0.86681 0.227013 0.389365 0.555042 0.61008

Signf 0.951129 0.006765 0.193903 0.265909 0.868682 , 0.025427 0.588749 0.340371 0.33148 0.38992n 8 8 6 7 8 8 6 8 8 5 4

LeadPore-water P Corr 0.035834 0.486315 0.619209 -0.01586 0.052046 -0.86681 1 -0.33141 0.475576 -0.32349 -0.70492

Signf 0.946272 0.328035 0.380791 0.979812 0.922002 0.025427 , 0.521081 0.340417 0.676512 0.501964n 6 6 4 5 6 6 6 6 6 4 3

Lead fish P Corr 0.072296 -0.18314 0.179443 -0.03016 0.035697 0.227013 -0.33141 1 0.520802 -0.0912 0.723638Signf 0.864917 0.664222 0.733725 0.948814 0.933125 0.588749 0.521081 , 0.185703 0.884045 0.276362n 8 8 6 7 8 8 6 8 8 5 4

15

Appendix 1: (continued)

Correlation Table pHpore-water

pHsediment

Cadmiumsediment

CadmiumPore-water

CadmiumClarias gariepinus

Leadsediment

LeadPore-water

LeadClarias gariepinus

Chromiumsediment

ChromiumPore-water

ChromiumClarias gariepinus

Chromiumsediment P Corr -0.32777 -0.40601 0.938908 -0.33586 0.484524 0.389365 0.475576 0.520802 1 0.578646 0.474685

n 8 8 6 7 8 8 6 8 8 5 4ChromiumPore-water P Corr -0.93477 -0.21539 0.633387 0.305405 0.904301 0.555042 -0.32349 -0.0912 0.578646 1 1

Signf 0.019802 0.72789 0.563329 0.617279 0.035024 0.33148 0.676512 0.884045 0.306722 , ,n 5 5 3 5 5 5 4 5 5 5 2

Chromiumfish P Corr -0.97051 0.015536 0.438555 0.678704 0.575223 0.61008 -0.70492 0.723638 0.474685 1 1

Signf 0.02949 0.984464 0.710981 0.525084 0.424777 0.38992 0.501964 0.276362 0.525315 , ,n 4 4 3 3 4 4 3 4 4 2 4

16

Appendix 2: Cadmium levels

Pore-water Sediment Fish *BCF **BSAF

Sampling point (mg l-1) pH (mg kg-1) pH (mg kg-1)

Nasolo (BNC) 0.039 ±0.0032 7.610 ±0.095 ND 6.643 ±0.006 0.327 ±0.231 8.44 -

Nasolo (SRN) 0.057 ±0.001 6.457 ±0.006 0.103 ±0.005 6.977 ±0.006 0.945 ±0.006 16.67 9.17

Naperi (Rainbow) 0.061 ±0.001 7.333 ±0.005 0.012 ±0.000 6.780 ±0.053 0.102 ±0.001 1.67 8.53

Naperi (Moi Rd) ND 7.350 ±0.000 0.009 ±0.001 6.597 ±0.015 0.319±0.001 - 34.33

Limbe (Mpingwe) 0.043 ±0.001 7.607 ±0.012 ND 6.887 ±0.023 0.264 ±0.000 6.18 -

Limbe (High Way) 0.054 ±0.004 7.577 ±0.006 0.016 ±0.001 6.730 ±0.027 0.298 ±0.003 5.48 18.96

Mudi (MDI) 0.033 ±0.002 7.637 ±0.006 0.092 ±0.001 6.040 ±0.017 0.377 ±0.031 11.42 4.11

Mudi (SRN) 0.040 ±0.002 7.093 ±0.006 0.298 ±0.001 6.153 ±0.055 0.544 ±0.061 13.70 1.83

* BCF = Bioconcentration factor**BSAF = Biota to sediment accumulation factor

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Appendix3: Lead levels

Pore-water Sediment Fish BCF BSAF

Sampling point (mg l-1) pH (mg kg-1) pH (mg kg-1)

Nasolo (BNC) 0.039 ±0.003 7.610 ±0.095 ND 6.643 ±0.006 0.327 ±0.231 8.44 -

Nasolo (SRN) 0.057 ±0.001 6.457 ±0.006 0.103 ±0.005 6.977 ±0.006 0.945 ±0.006 16.67 9.17

Naperi (Rainbow) 0.061 ±0.001 7.333 ±0.006 0.012 ±0.000 6.780 ±0.053 0.102 ±0.001 1.67 8.53

Naperi (Moi Rd) ND 7.350 ±0.000 0.009 ±0.001 6.597 ±0.015 0.319 ±0.001 - 34.33

Limbe (Mpingwe) 0.043 ±0.001 7.607 ±0.012 ND 6.887 ±0.023 0.264 ±0.000 6.18 -

Limbe (High Way) 0.054 ±0.004 7.577 ±0.006 0.016 ±0.001 6.730 ±0.021 0.298 ±0.003 5.48 18.96

Mudi (MDI) 0.033 ±0.002 7.637 ±0.006 0.092 ±0.001 6.040 ±0.017 0.377 ±0.031 11.42 4.11

Mudi (SRN) 0.040 ±0.002 7.093 ±0.006 0.298 ±0.001 6.153 ±0.055 0.544 ±0.061 13.70 1.83

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Appendix 4: Chromium levels

Pore-water Sediment Fish BCF BSAF

Sampling point (mg l-1) pH (mg kg-1) pH (mg kg-1)

Nasolo (BNC) 0.039 ±0.003 7.610 ±0.095 ND 6.643 ±0.006 0.3267 ±0.231 8.44 -

Nasolo (SRN) 0.057 ±0.001 6.457 ±0.006 0.103 ±0.005 6.977 ±0.006 0.945 ±0.006 16.67 9.17

Naperi (Rainbow) 0.061 ±0.001 7.333 ±0.006 0.012 ±0.000 6.780 ±0.051 0.102 ±0.001 1.67 8.53

Naperi (Moi Rd) ND 7.350 ±0.000 0.009 ±0.001 6.597 ±0.015 0.319 ±0.001 - 34.33

Limbe (Mpingwe) 0.042 ±0.001 7.607 ±0.012 ND 6.887 ±0.023 0.264 ±0.000 6.18 -

Limbe (High Way) 0.054 ±0.004 7.577 ±0.006 0.016 ±0.001 6.730 ±0.027 0.298 ±0.003 5.48 18.96

Mudi (MDI) 0.033 ±0.002 7.637 ±0.006 0.092 ±0.001 6.040 ±0.0173 0.377 ±0.031 11.42 4.11

Mudi (SRN) 0.040 ±0.002 7.093 ±0.006 0.298 ±0.001 6.153 ±0.0551 0.544 ±0.061 13.70 1.83

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