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© 2024 by the authors; licensee Asian Online Journal Publishing Group 
 

Agriculture and Food Sciences Research 
Vol. 11, No. 2, 146-155, 2024 

ISSN(E) 2411-6653/ ISSN(P) 2518-0193 
DOI: 10.20448/aesr.v11i2.6228 

© 2024 by the authors; licensee Asian Online Journal Publishing Group 

 
 

 
 
 
Heavy metal accumulation in soil and leafy vegetables irrigated with domestic 
wastewater in Vietnam 

 
Pham Thi Thom1   

Nguyen Tuan Khoi2   

Phan Le Na3   

  
( Corresponding Author)  

1,2,3BacGiang Agriculture and Forestry University, Vietnam. 
1Email: thompt87@wru.vn  
2Email: khoint@bafu.edu.vn  
3Email: napl@bafu.edu.vn  

 
Abstract 

This study was conducted to evaluate the accumulation of heavy metals, including copper (Cu), 
lead (Pb), and cadmium (Cd), in soil and leafy vegetables irrigated with domestic wastewater. The 
surveyed vegetables included water spinach (Ipomoea aquatica), Chinese mustard greens (Brassica 
integrifolia), and Malabar spinach (Basella alba), grown over three consecutive seasons. Results 
showed that Cu accumulation in the vegetables ranged from 4.41 mg/kg to 5.62 mg/kg, Pb from 
0.11 mg/kg to 0.13 mg/kg, and Cd from 0.02 mg/kg to 0.03 mg/kg. All values were below the 
safety limits set by Vietnam’s National Technical Regulation (QCVN), with thresholds of 30 
mg/kg for Cu, 0.3 mg/kg for Pb, and 0.2 mg/kg for Cd. Similarly, heavy metal accumulation in 
the soil remained within the permissible limits under QCVN standards. The analysis further 
indicated that seasonal variations had minimal impact on heavy metal concentrations, suggesting 
that consistent wastewater management practices contributed to maintaining soil and crop safety. 
In addition, the research highlighted that water spinach accumulated slightly higher levels of 
heavy metals compared to the other vegetables, likely due to its faster growth rate and higher 
water absorption capacity. Despite this, the concentrations remained well within safety 
thresholds, affirming the viability of these crops for safe consumption. The study concludes that 
using domestic wastewater for vegetable irrigation does not lead to heavy metal accumulation 
beyond safe thresholds, supporting sustainable and safe agricultural practices. However, 
continued monitoring and appropriate wastewater treatment remain essential to ensure long-term 
safety, particularly as environmental and anthropogenic factors evolve. 

 
Keywords: Domestic wastewater irrigation, Environmental health risks, Food Safety and heavy metals, Heavy metal contamination, Leafy 
vegetable safety in Vietnam, Soil and plant health risks. 

 
Citation | Thom, P. T., Khoi, N. T., & Na, P. L. (2024). Heavy 
metal accumulation in soil and leafy vegetables irrigated with 
domestic wastewater in Vietnam. Agriculture and Food Sciences 
Research, 11(2), 146–155. 10.20448/aesr.v11i2.6228 
History:  
Received: 11 November 2024 
Revised: 9 December 2024 
Accepted: 12 December 2024 
Published: 20 December 2024 
Licensed: This work is licensed under a Creative Commons 

Attribution 4.0 License  
Publisher:  Asian Online Journal Publishing Group 

Funding: This study received no specific financial support 
Institutional Review Board Statement: Not applicable. 
Transparency: The authors confirm that the manuscript is an honest, 
accurate, and transparent account of the study; that no vital features of the 
study have been omitted; and that any discrepancies from the study as 
planned have been explained. This study followed all ethical practices during 
writing. 
Competing Interests: The authors declare that they have no competing 
interests. 
Authors’ Contributions: All authors contributed equally to the conception 
and design of the study. All authors have read and agreed to the published 
version of the manuscript. 

 
Contents 
1. Introduction .................................................................................................................................................................................... 147 
2. Content and Research Methodology .......................................................................................................................................... 147 
3. Research Results ............................................................................................................................................................................ 148 
4. Conclusion ....................................................................................................................................................................................... 153 
References ............................................................................................................................................................................................ 153 
 

 

 

 

mailto:thompt87@wru.vn
mailto:khoint@bafu.edu.vn
mailto:napl@bafu.edu.vn
https://creativecommons.org/licenses/by/4.0/
https://creativecommons.org/licenses/by/4.0/
https://www.doi.org/10.20448/aesr.v11i2.6228
https://orcid.org/0009-0008-3017-8738
https://orcid.org/0000-0002-5920-1486
https://orcid.org/0009-0002-5198-7485


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Contribution of this paper to the literature 
This study contributes to sustainable agriculture by demonstrating that domestic wastewater 
can be safely used for irrigating leafy vegetables without exceeding heavy metal safety 
thresholds. It highlights the potential for resource optimization, provides baseline data for safe 
wastewater reuse practices, and underscores the importance of monitoring to ensure long-term 
environmental and food safety. 

 
1. Introduction 

In the context of freshwater scarcity, the reuse of domestic wastewater in agriculture has emerged as a 
potential solution to meet irrigation demands and alleviate pressure on freshwater resources [1]. However, 
domestic wastewater may contain heavy metals such as copper (Cu), lead (Pb), and cadmium (Cd) [2] which are 
elements capable of accumulating in soil and crops [3] posing potential risks to agricultural product quality and 
human health if they exceed safe limits [4]. These heavy metals can be toxic in the environment, reducing crop 
yields and posing health risks if they enter the food chain [5]. Leafy vegetables, which are often consumed directly 
[6] present a particular concern regarding heavy metal accumulation from soil and irrigation water, necessitating 
rigorous assessment [7]. This study aims to evaluate the accumulation levels of Cu, Pb, and Cd in soil and leafy 
vegetables irrigated with domestic wastewater over three consecutive growing seasons. The selected vegetables 
include water spinach (Ipomoea aquatica), Chinese mustard greens (Brassica integrifolia), and Malabar spinach 
(Basella alba). The accumulation levels of Cu, Pb, and Cd in both the vegetables and soil will be compared to the 
safety limits set by Vietnam’s National Technical Regulation (QCVN), thereby assessing the safety and feasibility 
of applying domestic wastewater in agriculture. 

 

2. Content and Research Methodology 
2.1. Research Content 

This study assesses the accumulation of heavy metals in leafy vegetables and soil when irrigated with domestic 
wastewater. The vegetables examined include water spinach (Ipomoea aquatica), Chinese mustard greens (Brassica 
integrifolia), and Malabar spinach (Basella alba). Domestic wastewater is collected from ponds that receive 
discharge from surrounding households and then used to irrigate the vegetables in the experiment. The objective is 
to determine the heavy metal accumulation in both vegetables and soil over different planting seasons. 
 
2.2. Research Methodology 
2.2.1. Experimental Design 

Subjects: Three types of leafy vegetables: water spinach, Chinese mustard greens, and Malabar spinach. 
Experimental Period: Conducted over three planting seasons: 
Season 1: Starting June 1, 2022. 
Season 2: Starting August 10, 2022. 
Season 3: Starting October 15, 2022. 
Replications: Each vegetable type is grown in three replicates (3 plots per vegetable). Experimental plots are 

arranged randomly. 
 

2.2.2. Sample Collection and Analysis 
After each planting season, samples of both vegetables and soil are collected from the experimental plots. 

Random samples are taken from the three replicates of each vegetable type to calculate the mean values of the 
parameters. 

Sample collection and preparation for vegetables follow TCVN 9016:2011. 
Soil sampling, preservation, and preparation adhere to standards: TCVN 7538-2:2005 (ISO 10381-2:2002). 
Heavy metal content in vegetable and soil samples is analyzed using atomic absorption spectroscopy (AAS) as 

per TCVN 6496:2009. 
 

2.2.3. Data Analysis Method 
Data are analyzed by calculating the mean values of parameters across replicates for each vegetable and season. 
SPSS statistical software is used to assess the differences in heavy metal content between vegetable types and 

planting seasons. 
Table 1 presents the analysis results of domestic wastewater samples utilized for vegetable irrigation. 
 

Table 1. Analysis results of domestic wastewater samples used for vegetable irrigation. 

Indicator Parameter QCVN 08-MT:2015/BTNMT 

Temperature (°C) 24.42 ± 0.37 - 
pH 7.52 ± 0.14 5.5-9 
Total suspended solids (TSS) (mg/l) 482.6 ± 14.3 50 
Electrical conductivity (EC) (mS/cm) 0.59 ± 0.01 - 

Ammonium (NH₄⁺-N) (mg/l) 5.12 ± 0.14 0.9 

Phosphate (PO₄³⁻-P) (mg/l) 1.58 ± 0.07 0.3 

Dissolved Oxygen (DO) (mg/l) 3.08 ± 0.17 ≥ 4 
Turbidity (NTU) 79.2 ± 2.72 - 
Cadmium (Cd) (mg/l) 0.032 ± 0.0005 0.01 
Copper (Cu) (mg/l) 0.019 ± 0.0005 0.5 
Lead (Pb) (mg/l) 0.03± 0.0006 0.05 
Note: QCVN: Vietnam’s national technical regulation. 

BTNMT: Ministry of natural resources and environment. 



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3. Research Results 
The wastewater analysis indicates several parameters exceeding the acceptable limits set by the Ministry of 

Natural Resources and Environment (QCVN 08-MT:2015/BTNMT), meaning they do not meet the required 

safety standards for irrigation. Specifically, TSS is at 482.6 mg/l, far above the permissible 50 mg/l. NH₄⁺-N is 

measured at 5.12 mg/l, surpassing the limit of 0.9 mg/l, and PO₄³⁻-P is 1.58 mg/l, exceeding the allowed 0.3 mg/l. 
Additionally, Cd at 0.032 mg/l is above the limit of 0.01 mg/l. DO at 3.08 mg/l falls below the required minimum 
of ≥4 mg/l. In contrast, Pb at 0.03 mg/l and Cu at 0.019 mg/l are within safe limits, meeting the standard 
requirements. These results highlight the need for treatment to reduce TSS, ammonium, phosphate, and cadmium 
levels to comply with safety standards before irrigation use.  

Table 2 illustrates the impact of domestic wastewater irrigation on copper (Cu) accumulation in leafy 
vegetables. 
 
Table 2. Impact of domestic wastewater on Cu accumulation in leafy vegetables. 

Vegetable varieties 
The first 
season 

The second 
season 

The third 
season 

Average 
Regulations 

according to QCVN 

Water spinach 5.57 ± 0.26 5.36 ± 0.27 5.11 ± 0.1 5.35± 0.28 
30 Chinese mustard greens 5.9 ± 0.28 5.6 ± 0.34 5.57 ± 0.21 5.62 ± 0.25 

Malabar spinach 4.43 ± 0.11 4.31 ± 0.22 4.48 ± 0.22 4.41 ± 0.18 
Note: (Unit: mg/kg dry vegetable). 

QCVN: Vietnam’s national technical regulation. 

 
Excessive copper (Cu) accumulation in leafy vegetables poses serious health risks due to its potential toxicity 

[8]. While Cu is an essential micronutrient in small amounts, high concentrations can disrupt cellular processes by 
generating reactive oxygen species (ROS), damaging plant tissues and reducing crop yield [9]. In humans, chronic 
exposure to elevated Cu levels through food consumption may lead to symptoms such as gastrointestinal distress, 
liver dysfunction, and, in severe cases, liver diseases [10]. 

Studies show that leafy vegetables like spinach can absorb substantial amounts of Cu when grown in 
contaminated soils or irrigated with Cu-laden wastewater [11]. In regions with high levels of Cu contamination, 
concentrations in vegetables often exceed safe limits set by the World Health Organization (WHO), thus 
increasing the risk of bioaccumulation and adverse health effects [12]. 

This issue is especially concerning in areas where untreated wastewater is used for irrigation, emphasizing the 
need for stringent monitoring and improved agricultural practices to prevent Cu-related health hazards in the food 
supply [13].  

The study on copper (Cu) accumulation in three types of leafy vegetables—water spinach (Ipomoea aquatica), 
Chinese mustard greens (Brassica integrifolia), and Malabar spinach (Basella alba)—was conducted over three 
growing seasons with these vegetables irrigated using domestic wastewater. Results indicate that Cu accumulation 
in all these vegetables remained below the permissible limits set by the National Technical Regulation on heavy 
metal limits in food (QCVN), which specifies a maximum threshold for copper at 30 mg/kg. 

Figure 1 Compares copper (Cu) accumulation in leafy vegetables irrigated with domestic wastewater against 
Vietnamese safety standards. 

 

 
Figure 1. Comparison of Cu accumulation in leafy vegetables with Vietnamese standards. 

Note: QCVN: Vietnamese national technical regulations. 
 

 
Specifically, over the three growing seasons, water spinach exhibited an average Cu accumulation of 5.35 ± 

0.28 mg/kg, Chinese mustard greens 5.62 ± 0.25 mg/kg, and Malabar spinach 4.41 ± 0.18 mg/kg. In individual 
seasons, Cu accumulation in water spinach ranged from 5.11 mg/kg to 5.57 mg/kg, in Chinese mustard greens 
from 5.57 mg/kg to 5.9 mg/kg, and in Malabar spinach from 4.31 mg/kg to 4.48 mg/kg. Chinese mustard greens 
showed the highest Cu accumulation, especially in the first season at 5.9 mg/kg, while Malabar spinach 
consistently had the lowest accumulation across all seasons, with an average of only 4.41 mg/kg. 



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Although there are some differences in Cu accumulation among the vegetable types, the variation is not 
substantial. Chinese mustard greens tend to absorb more Cu compared to water spinach and Malabar spinach, but 
all three vegetables maintained safe Cu accumulation levels, significantly below the maximum threshold of 30 
mg/kg set by QCVN. This indicates that, under experimental conditions, the use of domestic wastewater for 
irrigating leafy vegetables does not lead to a significant increase in copper accumulation that would pose health 
risks to consumers. 

 
Table 3. presents the impact of domestic wastewater on Pb accumulation in leafy vegetables. 

Vegetable varieties 
The first 
season 

The second 
season 

The third 
season 

Average 
Regulations 
according to 

QCVN 

Water spinach 0.12 ± 0.006 0.13 ± 0.006 0.12 ± 0.01 0.12± 0.007 
0.3 Chinese mustard greens 0.12 ± 0.006 0.13 ± 0.006 0.15 ± 0.006 0.13± 0.014 

Malabar spinach 0.12 ± 0.006 0.11 ± 0.006 0.11± 0.006 0.11± 0.007 
Note: (Unit: mg/kg dry vegetable). 

QCVN: Vietnam’s national technical regulation. 

 
Lead (Pb) accumulation in leafy vegetables and domestic wastewater poses significant health and 

environmental risks [14]. Pb is a toxic heavy metal with no known biological function in plants or humans [15]. 
Its presence in soil and water sources, often due to industrial activities and urban runoff, leads to absorption by 
plants, especially leafy vegetables, through both roots and foliage exposed to contaminated water and atmospheric 
particles [16]. When Pb concentrations exceed the World Health Organization’s safety limits, its consumption 
through contaminated vegetables can result in serious health consequences, including neurological damage, kidney 
dysfunction, and developmental issues, particularly in young children [1]. 

In domestic wastewater, Pb can accumulate from various sources, including plumbing, industrial discharge, and 
household products [2]. When this wastewater is used for irrigation without adequate treatment, it increases Pb 
levels in the soil, which plants readily absorb [3]. This cycle not only impacts food safety but also threatens soil 
health, as Pb can persist in the environment, leading to long-term ecological contamination [17]. These risks 
highlight the critical need for managing Pb in wastewater and ensuring it does not enter the agricultural food 
chain [18]. 

Table 3 assessed the accumulation of lead (Pb) in leafy vegetables, including water spinach, Chinese mustard 
greens, and Malabar spinach, when irrigated with domestic wastewater over three growing seasons. The results 
indicate that Pb levels in all vegetable samples remained within the safety limits set by the National Technical 
Regulation (QCVN) for heavy metal limits in food, with a maximum threshold for Pb at 0.3 mg/kg. 

Figure 2 compares Pb accumulation in leafy vegetables irrigated with domestic wastewater to Vietnamese 
safety standards. 

 

 
Figure 2. Comparison of Pb accumulation in leafy vegetables with Vietnamese standards. 

 
The Pb content in water spinach fluctuated slightly across the seasons, with values of 0.12 ± 0.006 mg/kg in 

the first and third seasons and 0.13 ± 0.006 mg/kg in the second season, averaging 0.12 ± 0.007 mg/kg. Chinese 
mustard greens exhibited slightly higher Pb accumulation than water spinach, ranging from 0.12 ± 0.006 mg/kg 
in the first season, 0.13 ± 0.006 mg/kg in the second, and peaking at 0.15 ± 0.006 mg/kg in the third season, with 
an average of 0.13 ± 0.014 mg/kg. For Malabar spinach, Pb levels were more stable and lower than in the other 
vegetables, ranging from 0.11 ± 0.006 mg/kg in the second and third seasons to 0.12 ± 0.006 mg/kg in the first 
season, averaging 0.11 ± 0.007 mg/kg. 

A comparison across the three vegetables shows that Chinese mustard greens had the highest Pb accumulation, 
particularly in the third season at 0.15 mg/kg, while Malabar spinach had the lowest accumulation across all 



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seasons. However, these differences are minimal, and all values are well below the maximum threshold of 0.3 
mg/kg set by QCVN. 

These results indicate that, although domestic wastewater may contain Pb, the accumulation levels in leafy 
vegetables grown under the study conditions remain safe and do not exceed permissible limits. 

Table 4 demonstrates the impact of domestic wastewater irrigation on Cd accumulation in leafy vegetables. 

 
Table 4. Impact of domestic wastewater on Cd accumulation in leafy vegetables. 

Vegetable varieties 
The first 
season 

The second 
season 

The third 
season 

Average 
Regulations 

according to QCVN 

Water spinach 0.03 ± 0.006 0.03 ± 0.006 0.03 ± 0.006 0.03 ± 0.005 
0.2 Chinese mustard greens 0.03 ± 0.006 0.03 ± 0.006 0.03 ± 0.006 0.03 ± 0.005 

Malabar spinach 0
 

0.03 ± 0.006 0.03 ± 0.006 0.02 ± 0.004 
Note: (Unit: mg/kg dry vegetable). 

QCVN: Vietnam’s national technical regulation. 

 
The accumulation of cadmium (Cd) in leafy vegetables and domestic wastewater poses serious health hazards to 

humans [19]. Cd is a toxic heavy metal that, unlike essential nutrients, serves no beneficial role in biological 
systems [20]. When Cd enters the food chain through contaminated leafy vegetables, it can lead to severe health 
issues [21]. Long-term ingestion of Cd-contaminated foods can result in kidney damage, osteoporosis, and even 
cancer due to Cd's high toxicity and tendency to accumulate in the body over time [22]. 

In domestic wastewater, Cd often originates from industrial waste, batteries, and household products [23]. 
When such wastewater is used for irrigation, Cd can be transferred to the soil and then taken up by plants, 
especially leafy vegetables, which are prone to heavy metal accumulation [24]. This cycle not only increases Cd 
concentrations in edible crops but also creates persistent contamination in agricultural soil [25]. The risks 
associated with Cd accumulation underline the necessity for effective wastewater treatment and regular monitoring 
to protect public health and ensure safe food production [26]. In the study on cadmium (Cd) accumulation in three 
types of leafy vegetables—water spinach, Chinese mustard greens, and Malabar spinach—irrigated with domestic 
wastewater over three growing seasons, results consistently showed that Cd accumulation levels remained within 
the safe limits set by the National Technical Regulation (QCVN), which specifies a maximum threshold for Cd at 
0.3 mg/kg. Figure 3 compares Cd accumulation in leafy vegetables irrigated with domestic wastewater against 
Vietnamese safety standards. 

 

 
Figure 3. Comparison of Cd accumulation in leafy vegetables with Vietnamese standards. 

 
Water spinach showed stable Cd accumulation across the three seasons, with values of 0.03 ± 0.006 mg/kg in 

each season and an average of 0.03 ± 0.005 mg/kg. Similarly, Chinese mustard greens also exhibited steady Cd 
levels, ranging around 0.03 ± 0.006 mg/kg in each season, averaging 0.03 ± 0.005 mg/kg. Malabar spinach, 
however, showed a slight variation, with no detectable Cd accumulation in the first season (0 mg/kg), increasing to 
0.03 ± 0.006 mg/kg in the second and third seasons, resulting in a three-season average of 0.02 ± 0.004 mg/kg. 

Comparing the vegetables, both water spinach and Chinese mustard greens showed similar Cd accumulation 
across all seasons, while Malabar spinach had significantly lower levels in the first season. Nonetheless, this 
difference holds little significance for food safety, as all values were well below the QCVN safety threshold of 0.3 
mg/kg. 

 
Table 5. Shows the impact of domestic wastewater irrigation on Cu accumulation in soil. 

Vegetable varieties 
The first 
season 

The second 
season 

The third 
season 

Average 
Regulations 

according to QCVN 

Water spinach 23.62 ± 1.13 24.15 ± 0.49 23.81 ± 1.09 23.86 ± 0.85 
100 Chinese mustard greens 23.62 ± 1.13 24.08 ± 0.43 23.88 ± 0.98 23.86 ± 0.81 

Malabar spinach 23.69 ± 0.49 24.21 ± 0.38 23.83 ± 0.46 23.91 ± 0.45 
Note: (Unit: mg/kg). 

QCVN: Vietnam’s national technical regulation. 



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Copper (Cu) accumulation in agricultural soil poses significant risks to both plant health and human safety. In 
soil, excessive Cu levels can lead to phytotoxicity, disrupting key plant processes like photosynthesis and enzyme 
activity, ultimately reducing crop yield and quality [27]. Cu’s high affinity for binding to soil particles also means 
it can persist in the environment, gradually building up to toxic levels in areas subjected to repeated Cu exposure 
from fertilizers or wastewater irrigation [28]. 

For plants, Cu toxicity often manifests in stunted growth, leaf discoloration, and reduced root development, as 
high Cu concentrations interfere with nutrient absorption [29]. When leafy vegetables are grown in Cu-
contaminated soil, they tend to absorb and accumulate Cu in their tissues, which can be transferred to humans 
through consumption [30]. Long-term exposure to elevated Cu levels in food has been associated with 
gastrointestinal distress, liver toxicity, and, in severe cases, neurological impacts [31]. 

These potential health effects highlight the need for careful Cu management in agricultural soils to protect 
both environmental and public health [32]. 

Table 5 presents data on the impact of domestic wastewater on copper (Cu) accumulation in soil used to grow 
leafy vegetables, including water spinach, Chinese mustard greens, and Malabar spinach, over three planting 
seasons. The results indicate that Cu accumulation in soil ranged from 23.62 ± 1.13 mg/kg to 24.21 ± 0.38 mg/kg, 
with average values between 23.86 ± 0.85 mg/kg and 23.91 ± 0.45 mg/kg. Compared to the Vietnamese National 
Technical Regulation (QCVN), which sets the maximum allowable Cu level in soil at 100 mg/kg, all Cu 
accumulation values in the soil for the three vegetables remained well below this limit, with averages significantly 
lower than the regulated threshold. 

Figure 4 illustrates Cu accumulation in soil irrigated with domestic wastewater compared to QCVN standards. 

 

 
Figure 4. Cu accumulation in soil with domestic wastewater irrigation compared to QCVN. 

Note: QCVN: Vietnam’s national technical regulation. 

 
Cu accumulation showed minor seasonal fluctuations, with standard deviations ranging from 0.38 mg/kg to 

1.13 mg/kg, indicating stability in the accumulation process. Malabar spinach showed the least variation, while 
water spinach and Chinese mustard greens exhibited slightly higher fluctuations but remained within safe levels. 
These results demonstrate that using domestic wastewater for soil irrigation does not lead to excessive Cu 
accumulation, ensuring safety for the soil ecosystem and crop health. 

Table 6 details the impact of domestic wastewater irrigation on Pb accumulation in soil. 
 
Table 6. Impact of domestic wastewater on Pb accumulation in soil. 

Vegetable varieties 
The first 
season 

The second 
season 

The third 
season 

Average 
Regulations 

according to QCVN 

Water spinach 1.9 ± 0.07 1.86± 0.11 1.92± 0.04 1.89 ± 0.07 
70 Chinese mustard greens 1.93 ± 0.16 1.62 ± 0.17 1.76 ± 0.2 1.77 ± 0.2 

Malabar spinach 1.82 ± 0.12 1.8 ± 0.08 1.88 ± 0.13 1.83 ± 0.11 
Note: (Unit: mg/kg). 

QCVN: Vietnam’s national technical regulation. 

 



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Lead (Pb) accumulation in agricultural soil, particularly from the use of untreated domestic wastewater for 
irrigation, presents severe risks to both crops and human health [33]. Pb is a highly toxic heavy metal with no 
essential role in biological processes, and its persistence in soil means it can build up over time, especially when 
wastewater containing Pb residues is repeatedly used for irrigation [33]. In soil, Pb binds tightly to particles, 
making it challenging to remove and allowing it to be absorbed by plant roots [34]. When vegetables absorb Pb 
from contaminated soil, they become vectors of Pb exposure for humans, who may ingest the metal through their 
diet [35]. 

Ingesting Pb-contaminated vegetables can lead to a range of health problems, from developmental delays and 
neurological damage in children to kidney dysfunction and cardiovascular issues in adults [36]. Because Pb is not 
readily excreted from the body, it accumulates over time, causing long-term health impacts, particularly when 
exposure occurs regularly [37]. This risk underlines the importance of proper wastewater treatment and soil 
monitoring to ensure safe levels of heavy metals in agricultural soils and prevent Pb from entering the food chain 
[38]. 

Pb accumulation in the soil ranged from 1.62 mg/kg to 1.93 mg/kg, with an average of 1.89 ± 0.07 mg/kg for 
water spinach, 1.77 ± 0.2 mg/kg for Chinese mustard greens, and 1.83 ± 0.11 mg/kg for Malabar spinach. 
Compared to the Vietnamese National Technical Regulation (QCVN) limit of 70 mg/kg for Pb in soil, all Pb 
accumulation values were significantly below the safety threshold. 

Figure 5 illustrates Pb accumulation in soil irrigated with domestic wastewater compared to QCVN standards. 
 

 
Figure 5. Pb Accumulation in soil with domestic wastewater irrigation compared to QCVN. 

Note: QCVN: Vietnam’s national technical regulation. 

 
Seasonal fluctuations in Pb levels were minimal, with Chinese mustard greens showing the most variation and 

Malabar spinach the most stability. These results indicate that the use of domestic wastewater for irrigation does 
not result in significant Pb accumulation in soil, keeping Pb content well within the safe limits set by QCVN. Thus, 
domestic wastewater can be safely utilized in agricultural production without posing a risk of excessive Pb 
accumulation. 

Table 7 presents the impact of domestic wastewater irrigation on Cd accumulation in soil. 
 
Table 7. Impact of domestic wastewater on Cd accumulation in soil. 

Vegetable varieties 
The first 
season 

The second 
season 

The third 
season 

Average 
Regulations 

according to QCVN 

Water spinach 0.1 ± 0.06 0.1 ± 0.06 0.2 ± 0.06 0.13 ± 0.05 
1.5 Chinese mustard greens 0.2 ± 0.06 0.2 ± 0.06 0.2 ± 0.06 0.15 ± 0.07 

Malabar spinach 0.2 ± 0.06 0.1 ± 0.06 0.2 ± 0.06 0.17 ± 0.07 
Note: (Unit: mg/kg). 

QCVN: Vietnam’s national technical regulation. 

 
Cadmium (Cd) accumulation in soil used for vegetable cultivation presents significant health and 

environmental risks, particularly when domestic wastewater is used for irrigation [39]. Cd is a toxic heavy metal 
with no beneficial role in plants or animals and is known for its persistence and bioaccumulation potential in soil 
[40]. Over time, soils irrigated with Cd-contaminated water sources, such as untreated wastewater, can accumulate 
Cd to levels that impact both plant health and the safety of food produced in these soils [41].  



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In plants, Cd disrupts growth by interfering with essential nutrient absorption and generating reactive oxygen 
species (ROS), which damage cellular structures [42]. Leafy vegetables, in particular, tend to absorb and 
concentrate Cd in their tissues, making them significant sources of Cd exposure when consumed [43]. Chronic 
ingestion of Cd through contaminated vegetables can lead to serious health issues in humans, including kidney 
damage, bone demineralization, and increased cancer risk [44]. The persistence of Cd in soils further compounds 
these risks, as it accumulates over time, presenting a continuous hazard for crops and consumers alike [45].  

Cd levels ranged from 0.1 mg/kg to 0.2 mg/kg, with an average of 0.13 ± 0.05 mg/kg for water spinach, 0.15 
± 0.07 mg/kg for Chinese mustard greens, and 0.17 ± 0.07 mg/kg for Malabar spinach. Compared to the 
Vietnamese National Technical Regulation (QCVN), which sets a maximum permissible limit of 1.5 mg/kg for Cd 
in soil, all Cd accumulation values remained well below this threshold. Seasonal variations in Cd content were 
minimal, indicating stable accumulation levels in soil irrigated with domestic wastewater.  
Figure 6 depicts Cd accumulation in soil irrigated with domestic wastewater compared to QCVN standards. 

 

 
Figure 6. Cd accumulation in soil with domestic wastewater irrigation compared to QCVN. 

Note: QCVN: Vietnam’s national technical regulation. 

 
These results demonstrate that using domestic wastewater for irrigation does not lead to excessive Cd 

accumulation in soil, ensuring no harm to the soil environment or crops. Therefore, domestic wastewater use in 
agriculture can be considered sustainable and safe concerning heavy metal accumulation in soil. 
 

4. Conclusion 
The research results indicate that the accumulation levels of Cu, Pb, and Cd in soil and leafy vegetables 

irrigated with domestic wastewater are within the safety limits specified by Vietnam's National Technical 
Regulation (QCVN). Specifically, Cu accumulation in vegetables ranged from 4.41 mg/kg to 5.62 mg/kg, Pb from 
0.11 mg/kg to 0.13 mg/kg, and Cd from 0.02 mg/kg to 0.03 mg/kg, all significantly below the QCVN safety 
thresholds of 30 mg/kg for Cu, 0.3 mg/kg for Pb, and 0.2 mg/kg for Cd. 

Similarly, in soil, Cu accumulation ranged from 23.86 mg/kg to 23.91 mg/kg, Pb from 1.77 mg/kg to 1.89 
mg/kg, and Cd from 0.13 mg/kg to 0.17 mg/kg, all well within the regulatory limits established by QCVN. These 
findings demonstrate that using domestic wastewater for leafy vegetable irrigation does not lead to excessive heavy 
metal accumulation in vegetables or soil, ensuring safety for crops and soil ecosystems. 

This study thus confirms the feasibility of reusing domestic wastewater in agriculture. Utilizing domestic 
wastewater not only helps reduce the pressure on freshwater resources but also maintains sustainability and safety 
in agricultural production. 

 

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https://doi.org/10.3390/life12030339
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