Abstract
Non-treated wastewater is used for irrigation of aquatic food production systems in the peri-urban
areas of the major cities in Southeast Asia. Therefore concern is that potentially toxic elements
(PTEs) may accumulate in foods produced. Hanoi and Phnom Penh, the capitals of Vietnam and
Cambodia, respectively are examples of cities where aquatic food production systems are fed with
untreated wastewater.
In Hanoi, domestic and industrial wastewater is discharged to small natural rivers which flow to
districts south of the city where wastewater is pumped from the rivers into canals and is distributed
to aquatic vegetable and fish production systems. Fish is produced in ponds whereas aquatic
vegetables are produced in flooded fields. The use of wastewater for aquatic food production is less
organized in Phnom Penh. Here, domestic and industrial wastewater is discharged to canals which
flow out of the city where it is pumped into the 3,200 ha Cheung Ek Lake located south of the city.
The lake serves as site for natural treatment before the wastewater leaves the lake through a stream
and ends up in Basak River. Many settlers have squatted at the banks of Cheung Ek Lake. They
make a livelihood from producing floating aquatic vegetables and from fishing in the lake. Water
spinach (Ipomoea aquatica Forssk.) is the most important vegetable produced by weight in the
wastewater exposed systems in Hanoi and Phnom Penh.
One of the objectives of the study was to determine PTE concentrations in water spinach, fish, soil
and sediment from wastewater-fed production systems in Hanoi and Phnom Penh. Another aim was
to assess the food safety risks of water spinach and fish with respect to PTEs. The third aim was to
assess PTE retention capacity of river sediment in Hanoi and the governing retention mechanisms,
that may prevent PTEs from entering the food production systems.
In Hanoi, water spinach and soil samples were collected in five production systems with different
degree of wastewater exposure; none, low and high. In Phnom Penh, water spinach and sediment
samples were collected along transects from the wastewater inlets in Cheung Ek Lake to a distance
of 600 m. Furthermore, samples were collected at the lake outlet and at a control site not exposed to
wastewater. Fish samples of the species common carp (Cyprinus carpio), silver carp
(Hypophthalmichthys molitrix) and tilapia (Orechromis niloticus) were collected in two wastewaterfed
ponds in Hanoi. In Phnom Penh, blackskin catfish (Clarias meladerma), snakehead (Channastriatus) and swamp eel (Monopterus albus) were collected in Cheung Ek Lake. Sediment samples
) and swamp eel () were collected in Cheung Ek Lake. Sediment sampleswere further collected in the wastewater receiving rivers in Hanoi and pore water was extracted
from the sediment under anaerobic conditions. Total concentrations of about 34 elements were
determined in water spinach, soil, sediment and pore water. Arsenic, Cd and Pb concentrations were
determined in liver, skin and muscle tissue of fish.
The maximum observed PTE concentrations in water spinach produced in wastewater-fed systems
in Hanoi and Phnom Penh were for As: 0.19; Cd: 0.032; Cu: 2.95; Ni: 0.412; Pb: 0.206 and Zn:
9.08 mg kg-1 f.w. The observed PTE water spinach concentrations in Hanoi and Phnom Penh were
within or only slightly above the concentration range observed for water spinach grown at
agricultural soil not exposed to wastewater in Malaysia. Water spinach grown at sites of high and
low wastewater exposure did not show a significantly higher accumulation of PTEs compared to
sites without wastewater exposure. In Phnom Penh, water spinach from Cheung Ek Lake had
elevated Be, Cd, Fe, Ni, La, Pb, Sb and Zn concentrations near the wastewater inlets compared to
concentrations at the lake outlet and at the control site. Water spinach consumption in Hanoi and
Phnom Penh resulted in an estimated intake of As, Cd, Pb and Zn amounting to less than 11% of the
tolerable intake for each element. The PTE content of water spinach in Hanoi and Cheung Ek Lake
in Phnom Penh constituted low food safety risks for consumers.
Arsenic, Cd and Pb concentrations in muscle, skin and liver of fish grown in wastewater-fed
systems in Hanoi and Phnom were low and in most cases below the detection limit. However, mean
Cd and Pb concentrations in liver of tilapia were 0.366 and 0.31 mg kg-1 f.w., respectively. Arsenic
concentrations in skin of tilapia had a mean of 0.15 mg kg-1 f.w. Mean concentrations of As, Cd and
Pb in skin of blackskin catfish caught in Phnom Penh had averages of 17.3, 0.456 and 0.41 mg kg-1
f.w., respectively. Consumption of muscle tissue from fish produced in wastewater-fed systems in
Hanoi and Phnom Penh resulted in an estimated As, Cd and Pb intake amounting to less than 9% of
the tolerable intake for each element. The As, Cd and Pb concentrations in fish from Hanoi and
Cheung Ek Lake in Phnom Penh constituted low food safety risks for consumers.
In Hanoi, soils from sites of none, low and high wastewater exposure showed no difference in PTE
concentrations. In contrast were PTE concentrations of Ba, Cd, Cu, Ni, Pb, Sb and Zn elevated at
the wastewater inlets in Cheung Ek Lake in Phnom Penh compared to concentrations at the lake
outlet and at the control site. Especially the Ba and Zn concentrations were high with maximum
concentrations of 688 and 857 mg kg-1 d.w., respectively. Sediment in the wastewater exposed
rivers of Hanoi was strongly polluted with As, Ba, Cd, Cu, Ni and Zn. The sediment concentrations
of Pb and Sb were also high. Of most concern was the observed Cd concentration in To Lich River
which has a maximum of 427 mg kg-1 d.w.
The Hanoi river sediment had a high retention capacity for PTEs. Logarithm to the maximum
observed distribution coefficients (log10Kd,obs) were for Cd: 5.70; Cr: 5.90; Cu: >6.60; Mo: 4.70; Pb:
7.01 and Zn: 6.62. Precipitation of PTEs as sulphides was likely to be the main retention
mechanism. The high retention capacity of the river sediment prevents major PTE transport to the
wastewater-fed aquatic food production systems in Hanoi.
| Original language | English |
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| Place of Publication | Copenhagen |
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| Publisher | Center for Skov, Landskab og Planlægning/Københavns Universitet |
| Number of pages | 140 |
| ISBN (Print) | 978-87-7611-212-7 |
| Publication status | Published - 2007 |
