2026-09-24T17:58:39Zhttps://univendspace.univen.ac.za/server/oai/requestoai:univendspace.univen.ac.za:11602/24742024-09-10T14:38:30Zcom_11602_1928com_11602_1914com_11602_1897com_11602_737col_11602_2140col_11602_738
Gitari, W. M.
Mudzielwana, R.
Ngure, V.
Sathekge, Salphinah Ntombikayise
2022
2023-05-29T06:28:15Z
2023-05-29T06:28:15Z
2023-05-19
Sathekge, S. N. (2022) Assessment of co-occurrence of cyanotoxins, toxic metals and anionic surfactants in irrigation water, agricultural soils and food crops. University of Venda. South Africa.<http://hdl.handle.net/11602/2474>.
http://hdl.handle.net/11602/2474
Sathekge SN. Assessment of co-occurrence of cyanotoxins, toxic metals and anionic surfactants in irrigation water, agricultural soils and food crops. []. , 2023 [cited yyyy month dd]. Available from: http://hdl.handle.net/11602/2474
Sathekge, S. N. (2023). <i>Assessment of co-occurrence of cyanotoxins, toxic metals and anionic surfactants in irrigation water, agricultural soils and food crops</i>. (). . Retrieved from http://hdl.handle.net/11602/2474
Sathekge, Salphinah Ntombikayise. <i>"Assessment of co-occurrence of cyanotoxins, toxic metals and anionic surfactants in irrigation water, agricultural soils and food crops."</i> ., , 2023. http://hdl.handle.net/11602/2474
TY - Dissertation
AU - Sathekge, Salphinah Ntombikayise
AB - Globally, the occurrence of cyanobacterial blooms in freshwater ecosystems has become a concern.
Cyanobacteria produces secondary metabolites, known as cyanotoxins that cause acute and chronic
poisoning in animals and humans. History of mining, industrial activities and poor maintenance of
wastewater treatment infrastructure are the main causes of the hyper-eutrophic conditions affecting
most dams in South Africa. The co-occurrence of multiple stressors in agricultural waters and soils
potentially pose a human and animal risk if contaminated water and plants are ingested.
The study investigated the co-existence of cyanotoxins, anionic surfactants and metal species in
irrigation water, agricultural soils and food crops and determine the health risks associated with
consuming cyanotoxins contaminated plants in the Crocodile (West) Marico Water Management
Area, which covers parts of Gauteng and Northwest Provinces. Lastly, the study assessed the
applicability of passive sampling technology in monitoring of cyanotoxins using DIAON HP20
resins as an adsorbent. Water, food crops and soil samples were collected from Roodeplaat and
Hartbeespoort dam sites in irrigation canals and cropping fields in June 2019, September 2019,
February 2020, and March 2021. Seven sites were selected for sampling of water for cyanotoxins,
anionic surfactants and toxic metals, while 4 farmland sites were selected for agricultural soils and
food crops in Roodeplaat and Hartbeespoort sites. Physicochemical parameters of the irrigation
water (pH, temperature, EC, TDS, DO), chlorophyll-a and dissolved nutrients were also monitored
using Spectrophotometer and Spectro-Quant® Merck Pharo 100 with the photo-metric test kits
from Merck, respectively. The levels of Microcystins (MCs), anionic surfactants, and metals were
detected and quantified using the ELISA method, anionic surfactant portable photometer and
inductively coupled plasma mass spectrometry (ICP- MS), respectively. The results are presented
for each chapters below.
The results for chapter 1 revealed the co-existence of cyanotoxins, metal species and anionic
surfactants in the irrigation water, and agricultural soils, across sampling sites, throughout sampling
period. The microcystins in irrigation water ranged from 0.00 to 15.57 μg/L. Total anionic
surfactants in irrigation water and agricultural soil ranged from 0.01 to 3.49 mg/L and 1.81 to 5.46
mg/kg, respectively. Among all the physicochemical parameters only pH (p = 0.624), TDS (p = -
0.466), EC (p = - 0.445), and turbidity (p = 0.521) correlated with MCs. Moreover, total anionic
surfactant showed to have positive moderate relationship with levels of MCs in irrigation water (p =
0.342). Metal species in irrigation water were decreased in the following order: Al > Mn > Fe > B >
Zn > Ni > Cu > Pb > Cr > As and were all below the maximum DWAF acceptable limit, implying
that the water was safe for irrigation use. Metal species in other soil sampling sites such as
16534.61 – 33285 mg/kg (Fe), 111.25 – 723.4 mg/kg (Cr),4.44 – 23.93 mg/kg (Pb), 0.80 – 9.70
mg/kg (As), 22.11 – 33.95 mg/kg (Cu), and 33.70 – 85.885 mg/kg (Ni) were above the maximum
limit set by DEA, USEPA, and FAO/WHO for agricultural use. Thus, soils from Roodeplaat and
Hartbeespoort farmland sites are contaminated by the mentioned metals.
The findings from the second chapter of results revealed the bio-accumulation of microcystins and
metals in food crops. The estimated daily intake (EDI) for MCs in all food crops for both adults and
children were below 0.04 μg/kg DW acceptable value set by World Health Organisation, implying
that the crops were safe for human consumption by adult and children population. Metal species
levels accumulated in plant samples collected from different sampling sites, showed that 0.21 to
10.80 mg/kg (Cr), 19.64 to 734.00 mg/kg (Fe), 5.45 to 76.80 mg/kg (Zn), 0.01 to 0.20 mg/kg (As),
0.96 to 60.40 mg/kg (Cu), and 0.10 to 0.70 mg/kg (Pb) were above the EU and FAO/WHO
guideline standards. Spearman correlation between metals in plants and water showed that only Pb
(p = 0.874) and As (p = 0.809) in irrigation water had a positive moderate association with metals in
plants collected from the sampling sites. The estimated daily intake (EDI) of metals via
consumption of the crops were found to be below the maximum tolerable daily intake (MTDI)
proposed for each metal. The translocation factors (TF) showed that only Cu and Cd were rapidly
transported to the plant’s edible parts from the soil. Moreover, target hazard quotient (THQ) for
each metal were below 1, indicating that consuming the food crops wont cause carcinogenic effect
to the adult population, while hazard index (HI) for other sites was found to be >1 for crop plants,
thus plants from these sites pose a health hazards to adult population. In addition, the target cancer
risk (TCR) value for Cr and Ni in crops from other sampling sites were above the maximum
threshold implying that there is a potential cancer risk to adult population over a long-term.
In addition, findings from the third chapter showed that SPATT was applicable in monitoring and
detecting MCs across all sampling sites and sampling months. The MCs levels in grab and SPATT
bags ranged from 0.14 to 13.03 μg/L and 0.99 to 2.28 ng/g resin throughout the sampling sites and
months, respectively. Thus, showing the persistence of MCs in canals and farm dams of Roodeplaat
and Hartbeespoort. A spearman correlation revealed that pH (p = 0.776), Turbidity (p = 0.699) and
DO (p = 0.829) had a significant positive association with total toxins in grab samples, while total
dissolved MCs in SPATT samples showed negative moderate relationship with TDS (p = - 0.615)
and EC (p = - 0.602). Total toxin concentrations in SPATT bags and Grab samples did not show
any correlation this is because SPATT bags detect and collect microcystins within water column
overtime, unlike point (Grab sampling), hence, there is no relationship between the two-sampling
method. Overall results showed that SPATT bags with DIAON HP20 resin as an adsorbent proved
to be applicable in monitoring and detecting microcystins in the irrigation water of Roodeplaat and
Hartbeespoort sites.
DA - 2023-05-19
DB - ResearchSpace
DP - Univen
KW - Cyanobacteria
KW - Cyanotoxins
KW - Toxic metals
KW - Aniomic surfactants
KW - Irrigation water
KW - Agricultural soils
KW - Food crops
KW - Solid phase adsorption toxin tracking (SPATT)
LK - https://univendspace.univen.ac.za
PY - 2023
T1 - Assessment of co-occurrence of cyanotoxins, toxic metals and anionic surfactants in irrigation water, agricultural soils and food crops
TI - Assessment of co-occurrence of cyanotoxins, toxic metals and anionic surfactants in irrigation water, agricultural soils and food crops
UR - http://hdl.handle.net/11602/2474
ER -
Department of Geography and Environmental Sciences
Department of Geography and Environmental Sciences
Globally, the occurrence of cyanobacterial blooms in freshwater ecosystems has become a concern.
Cyanobacteria produces secondary metabolites, known as cyanotoxins that cause acute and chronic
poisoning in animals and humans. History of mining, industrial activities and poor maintenance of
wastewater treatment infrastructure are the main causes of the hyper-eutrophic conditions affecting
most dams in South Africa. The co-occurrence of multiple stressors in agricultural waters and soils
potentially pose a human and animal risk if contaminated water and plants are ingested.
The study investigated the co-existence of cyanotoxins, anionic surfactants and metal species in
irrigation water, agricultural soils and food crops and determine the health risks associated with
consuming cyanotoxins contaminated plants in the Crocodile (West) Marico Water Management
Area, which covers parts of Gauteng and Northwest Provinces. Lastly, the study assessed the
applicability of passive sampling technology in monitoring of cyanotoxins using DIAON HP20
resins as an adsorbent. Water, food crops and soil samples were collected from Roodeplaat and
Hartbeespoort dam sites in irrigation canals and cropping fields in June 2019, September 2019,
February 2020, and March 2021. Seven sites were selected for sampling of water for cyanotoxins,
anionic surfactants and toxic metals, while 4 farmland sites were selected for agricultural soils and
food crops in Roodeplaat and Hartbeespoort sites. Physicochemical parameters of the irrigation
water (pH, temperature, EC, TDS, DO), chlorophyll-a and dissolved nutrients were also monitored
using Spectrophotometer and Spectro-Quant® Merck Pharo 100 with the photo-metric test kits
from Merck, respectively. The levels of Microcystins (MCs), anionic surfactants, and metals were
detected and quantified using the ELISA method, anionic surfactant portable photometer and
inductively coupled plasma mass spectrometry (ICP- MS), respectively. The results are presented
for each chapters below.
The results for chapter 1 revealed the co-existence of cyanotoxins, metal species and anionic
surfactants in the irrigation water, and agricultural soils, across sampling sites, throughout sampling
period. The microcystins in irrigation water ranged from 0.00 to 15.57 μg/L. Total anionic
surfactants in irrigation water and agricultural soil ranged from 0.01 to 3.49 mg/L and 1.81 to 5.46
mg/kg, respectively. Among all the physicochemical parameters only pH (p = 0.624), TDS (p = -
0.466), EC (p = - 0.445), and turbidity (p = 0.521) correlated with MCs. Moreover, total anionic
surfactant showed to have positive moderate relationship with levels of MCs in irrigation water (p =
0.342). Metal species in irrigation water were decreased in the following order: Al > Mn > Fe > B >
Zn > Ni > Cu > Pb > Cr > As and were all below the maximum DWAF acceptable limit, implying
that the water was safe for irrigation use. Metal species in other soil sampling sites such as
16534.61 – 33285 mg/kg (Fe), 111.25 – 723.4 mg/kg (Cr),4.44 – 23.93 mg/kg (Pb), 0.80 – 9.70
mg/kg (As), 22.11 – 33.95 mg/kg (Cu), and 33.70 – 85.885 mg/kg (Ni) were above the maximum
limit set by DEA, USEPA, and FAO/WHO for agricultural use. Thus, soils from Roodeplaat and
Hartbeespoort farmland sites are contaminated by the mentioned metals.
The findings from the second chapter of results revealed the bio-accumulation of microcystins and
metals in food crops. The estimated daily intake (EDI) for MCs in all food crops for both adults and
children were below 0.04 μg/kg DW acceptable value set by World Health Organisation, implying
that the crops were safe for human consumption by adult and children population. Metal species
levels accumulated in plant samples collected from different sampling sites, showed that 0.21 to
10.80 mg/kg (Cr), 19.64 to 734.00 mg/kg (Fe), 5.45 to 76.80 mg/kg (Zn), 0.01 to 0.20 mg/kg (As),
0.96 to 60.40 mg/kg (Cu), and 0.10 to 0.70 mg/kg (Pb) were above the EU and FAO/WHO
guideline standards. Spearman correlation between metals in plants and water showed that only Pb
(p = 0.874) and As (p = 0.809) in irrigation water had a positive moderate association with metals in
plants collected from the sampling sites. The estimated daily intake (EDI) of metals via
consumption of the crops were found to be below the maximum tolerable daily intake (MTDI)
proposed for each metal. The translocation factors (TF) showed that only Cu and Cd were rapidly
transported to the plant’s edible parts from the soil. Moreover, target hazard quotient (THQ) for
each metal were below 1, indicating that consuming the food crops wont cause carcinogenic effect
to the adult population, while hazard index (HI) for other sites was found to be >1 for crop plants,
thus plants from these sites pose a health hazards to adult population. In addition, the target cancer
risk (TCR) value for Cr and Ni in crops from other sampling sites were above the maximum
threshold implying that there is a potential cancer risk to adult population over a long-term.
In addition, findings from the third chapter showed that SPATT was applicable in monitoring and
detecting MCs across all sampling sites and sampling months. The MCs levels in grab and SPATT
bags ranged from 0.14 to 13.03 μg/L and 0.99 to 2.28 ng/g resin throughout the sampling sites and
months, respectively. Thus, showing the persistence of MCs in canals and farm dams of Roodeplaat
and Hartbeespoort. A spearman correlation revealed that pH (p = 0.776), Turbidity (p = 0.699) and
DO (p = 0.829) had a significant positive association with total toxins in grab samples, while total
dissolved MCs in SPATT samples showed negative moderate relationship with TDS (p = - 0.615)
and EC (p = - 0.602). Total toxin concentrations in SPATT bags and Grab samples did not show
any correlation this is because SPATT bags detect and collect microcystins within water column
overtime, unlike point (Grab sampling), hence, there is no relationship between the two-sampling
method. Overall results showed that SPATT bags with DIAON HP20 resin as an adsorbent proved
to be applicable in monitoring and detecting microcystins in the irrigation water of Roodeplaat and
Hartbeespoort sites.
NRF
1 online resources (xiv, 170 leaves) : color illustrations, color maps
en
University of Venda
Cyanobacteria
UCTD
Cyanotoxins
Toxic metals
Aniomic surfactants
Irrigation water
Agricultural soils
Food crops
Solid phase adsorption toxin tracking (SPATT)
571.950968
Cyanobacteria -- South Africa
Cyanobacteria toxin -- South Africa
Irrigation water -- South Africa
Food crops -- South Africa
Assessment of co-occurrence of cyanotoxins, toxic metals and anionic surfactants in irrigation water, agricultural soils and food crops
Dissertation
open.access