Investigation on ratios of some common diseases and health risks relating to dioxin exposure in Da Nang, Vietnam

doi:10.21203/rs.3.rs-2064917/v2

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Investigation on ratios of some common diseases and health risks relating to dioxin exposure in Da Nang, Vietnam

https://doi.org/10.21203/rs.3.rs-2064917/v2

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Analyze the current status of disease patterns and health risks of people in Thanh Khe district (TK group) residing near areas where Agent Orange (AO)/dioxin was stored in Da Nang airport compared with people in Son Tra district (ST group - control group), Da Nang city. A cross-sectional descriptive study. This is a survey of 402 families residing in the TK group and 400 ones residing in the ST group. Subjects in the age group 45–69 accounted for a high proportion, of which women accounted for the majority, the residence time was stable and long, mainly over 15 years in both groups. People in the TK group had direct and indirect exposure to AO/dioxin accounted for a higher proportion than in the ST group. The incidence of some diseases that are recommended to be related to AO/dioxin such as hypertension (33.6%), diabetes mellitus (8.96%), and other diseases: stomach (23.0%), joints (40.3%), ear-nose-throat (ENT, 11.2%), urinary system (7.21%) compared with the ST group. Exposure to AO/dioxin has changed the disease pattern and increased some diseases in people residing near areas where AO/dioxin was previously stored.

Diseases

Health risks

AO/dioxin

Hot spot

Thanh Khe

Son Tra

During the war, from May 1964 to March 1972 at Da Nang airport, the US army stored and used 52.700 barrels of AO, 29.000 barrels of Agent White, and 5.000 barrels of Agent Blue for the spraying campaign “Ranch Hand” and the recovery campaign “Pacer Ivy” (Young 2009). Da Nang airport is one of the three most serious hot spots for dioxin contamination in Vietnam (Stellman et al. 2003; Dwernychuk 2005). The highest dioxin concentration recorded at the Da Nang airport reached 365.000 pg toxic equivalent (TEQ)/g in the soil in the former AO mixing and loading area (Hatfield Consultants and Office of the National Steering Committee 2009).

The Da Nang dioxin-contaminated sites were located north of the Da Nang airport in central Vietnam. Approximately 94.000 m³ of heavily dioxin-contaminated soil and sediment was treated between 2013 and 2017 by the environmental remediation project (Aspen Institute 2020). However, there is still 68.000 m³ of material with a concentration of less than 1.000 pg TEQ/g being landfilled in the southwest of the airport. People residing around Da Nang airport are at risk of dioxin exposure through ingestion, skin contact, and inhalation (USAID 2010; USAID 2018).

During the dioxin remediation project implementation, the residents living near the Da Nang airport were at low risk of being exposed to dioxin with an average daily dose through inhalation ranging from 0.006 to 0.129 pg TEQ/kg body weight/day, while residents living close to the former AO mixing and loading area faced elevated risks with an average daily dose was from 0.017 to 0.820 pg TEQ/kg body weight/day (Sau et al., 2021). Tuyet Hanh et al. estimated the daily intake of people living in 4 wards (An Khe, Hoa Khe, Chinh Gian, and Thac Gian) around Da Nang airport due to local high-risk food consumption was very large (from 27.0 to 148 pg TEQ/kg body weight/day), much higher than the World Health Organization (WHO) recommended tolerable daily intake (1 to 4 pg TEQ/kg body weight/day) (Tuyet Hanh et al. 2015). Recent studies have also shown that dioxin concentrations in the milk of mothers living in dioxin-exposed areas were higher than those of mothers living in non-dioxin-exposed areas (Wittsiepe et al. 2007; Todaka et al. 2010). The means of dioxin concentrations in breast milk collecting in 2008 and 2009 from mothers living around the former Da Nang hot spot were from 12.8 to 14.3 pg TEQ/g lipid (Tai et al. 2011).

AO/dioxin has strong, long-term, and serious effects on human health (Boivin and Minh 2015). It is capable of causing diverse and complex damage to all parts of the body such as cancer, damage to the skin, liver, thyroid, diabetes, the immune system, respiratory system, circulatory system, digestive system, endocrine system, nervous system, cardiovascular system, and lungs; causing mutations in genes and chromosomes, thereby causing birth defects and reproductive complications (Center for Health Environment and Justice 1999). The risk of dioxin exposure for people living near hot spots many years ago is very high. Therefore, this study investigated and compared the disease pattern and health risks of people in Thanh Khe district (TK group) living around previously heavily polluted areas with dioxin and local residents residing in Son Tra district (ST control group) far from Da Nang airport.

Study area

Da Nang is situated in the center of Viet Nam. Its mainland latitude and longitude are 15⁰55' to 16⁰14' N and 107⁰18' to 108⁰20' E. Da Nang city has a total area of 1.283 km² and had a population of 1.134.310 in 2019. The population density of Da Nang is about 883 people/km². Thanh Khe district has an area of only 9.36 km², a population of 178.447 people with the highest population density in the city: 19.065 people/km². Son Tra district has an area: 59.32 km², population: 132.944 people and population density: 2.241 people/km² (Da Nang Portal 2020).

TK group consisted of 402 households residing in four wards: An Khe, Hoa Khe, Chinh Gian, and Thac Gian (Fig. 1). This area has a very high risk of dioxin exposure because people live near areas previously heavily contaminated with AO/dioxin (Tuyet-Hanh et al. 2015).

ST group consisted of 400 households residing in three wards: An Hai Tay, An Hai Dong, and Phuoc My (Fig. 1). The ST group was similar to the TK group in terms of socio-economic conditions and population characteristics. Still, it was not directly affected by AO/dioxin residues inside Da Nang airport. ST group was located about 5 km east of Da Nang airport and across the Han River, unaffected by industrial activities.

Selection criteria

The subjects selected for the investigation were adults, of both sexes, aged between 18 and 69, representing each household, who had resided continuously in the locality for at least 5 years. During the survey, women were given priority to interview because they were subjects of reproductive health, often did housework, rarely had to work far away, therefore, had a really more stable and long-term residence time at the research location than men, especially women had less exposure to occupations with toxics in industry, household, and used alcohol, beer, and smoked less compared to men.

Study design and data collection

This is a cross-sectional descriptive biomedical study on the risk of dioxin exposure, health status and some diseases, and illnesses that may be related to dioxin exposure through questionnaires, face-to-face interviews, and statistical data.

We investigated general information, health status, risk factors for food consumption, history of exposure to AO/dioxin and toxic factors, medical history, and obstetric history related to dioxin exposure through an investigation form consisting of 85 questions in the form of a face-to-face interview. The interviewer had experience in the research field as well as clinical experience related to the investigated diseases.

People who were considered to have diseases were those who had had a confirmed test, had been treated in a hospital, were taking medication, or were receiving local outpatient treatment.

Investigation time

Time to conduct the survey in the TK group was in March 2021 and in the ST group was in October 2021.

Data analysis

Research data were processed by a computer using Excel 2013, IBM SPSS Statistics 20, and Statav4 software according to biomedical statistical methods. The results were presented as:

- Mean (X), percentage (%) and p < 0.05;
- Compared the ratios with the χ² test; The difference was statistically significant with p < 0.05.

Age distribution, residence time and sex distribution of the subjects

Table 1

Age distribution, residence time and sex distribution
Age group, residence time and sex		TK group (n = 402)		ST group (n = 400)		p
Age group, residence time and sex		Number of people	Rate (%)	Number of people	Rate (%)	p
Age group (years)	45–69	320	79.60	275	68.75	> 0.05
Age group (years)	18–44	82	20.40	125	31.25
Residence time	5–15 years	43	10.70	37	9.25
Residence time	Over 15 years	359	89.30	363	90.75
Sex	Men	120	29.85	130	32.50
Sex	Women	282	70.15	270	67.50

The mean age (mean ± 2SD) of the TK group was 53.83 ± 22.52 and of the ST group was 50.47 ± 24.42. In both groups, the age group 45–69 accounted for a high rate (TK: 79.60%, ST: 68.75%) and statistically significantly higher than in the age group 18–44 (TK: 20.4%, ST: 31.25%). (Table 1). However, within the same age group (18–44 or 45–69) there was no difference between the two groups (p > 0.05). This result showed that the TK group and the ST group were similar in age, consistent with the requirements for selecting subjects.

Table 1 also shows that the majority of households and people had long-term residence time, about over 15 years, in the two research locations with the rate of TK group: 89.30% and ST group: 90.75%. People with a residence period of 5–15 years only accounted for a low percentage (TK: 10.70%, ST: 9.25%) and there was no difference between the two groups (p > 0.05).

In both groups, women who were given priority to interview should make up the majority (TK: 70.15%, ST: 67.50%) and there was a statistically significant difference (p < 0.05) between the percentages of men and women in each group but no difference in sex ratio between the TK group and the ST group (p > 0.05) (Table 1).

Toxic elements and AO/dioxin exposure

Table 2

Exposure to toxic elements and AO/dioxin exposure
Toxic elements and type of exposure		TK group (n = 402)		ST group (n = 400)		p
Toxic elements and type of exposure		Number of people	Rate (%)	Number of people	Rate (%)	p
Toxic elements	Chemical fertilizers	3	0.75	3	0.75	> 0.05
	Pesticides, herbicides	3	0.75	3	0.75
	Pesticide poisoning	0	0	1	0.25
	Latex processing	0	0	3	0.75
	Wood processing	0	0	2	0.50
	Waste treatment/ incineration	1	0.25	2	0.50
	Cement	1	0.25	0	0
	Metallurgical	0	0	0	0
Types of exposure	Direct	14	3.48	0	0	< 0.05
Types of exposure	Indirect	38	9.45	7	1.75	< 0.05

The statistics in Table 2 show that the proportion of people exposed to toxic elements in industry and agriculture in the ST group and the TK group accounted for a very low percentage (less than 0.75%) and there was no difference reached statistical significance (p > 0.05) between the two groups.

In the TK group, the proportion of people directly and indirectly exposed to dioxins was 3.48% and 9.45%, respectively. These rates were statistically significantly higher (p < 0.05) than the ST group (0% and 1.75%, respectively). The ST group was far from the airport and no one in this group had ever worked in a hot spot or heavily contaminated area with dioxin, so there was no direct contact with dioxin (Table 2).

Status of living, alcohol, beer, and tobacco use

Table 3

Status of living, alcohol, beer, and tobacco use
Factors and stimulants		TK group (n = 402)		ST group (n = 400)		p
Factors and stimulants		Number of people	Rate (%)	Number of people	Rate (%)	p
Factors	Self-increasing	55	13.68	15	3.75	> 0.05
	Using tap water	402	100	400	100
	Food poisoning	55	13.68	29	7.25
Stimulants	Alcohol, beer	72	17.91	48	12.00	< 0.05
Stimulants	Tobacco	77	19.15	68	17.00	< 0.05

Table 3 shows that 100% of people in both groups used tap water for domestic use. The TK group had a self-increasing rate (growing more vegetables, raising poultry) of 13.7%, which was statistically significantly higher (p < 0.05) than the ST group (3.75%). The use of some foods that were self-increasing in areas at risk of dioxin exposure around Da Nang airport may be the reason why food poisoning in the TK group (13.7%) was higher and reached statistical significance compared to the ST group (7.25%).

Although there was no statistically significant difference (p > 0.05) in the status of alcohol, beer, and tobacco use of residents in the two groups, the rate of using alcohol, beer, and tobacco by residents in the TK group (17.91% and 19.15%, respectively) were higher than in the ST group (12.0% and 17.0%) (Table 3).

Disease pattern of subjects in the research location

Table 4

Disease pattern of subjects in the groups
Diseases	TK group (n = 402)		ST group (n = 400)		p
Diseases	Number of people	Rate (%)	Number of people	Rate (%)	p
Hypertension	135	33.58	76	19.00	< 0.05
Stomach	96	23.88	54	13.50	< 0.05
Joints	162	40.30	79	19.75	< 0.05
ENT	45	11.19	6	1.50	< 0.05
Liver and gallbladder	26	6.47	13	3.25	< 0.05
Kidney, urinary system	29	7.21	3	0.75	< 0.05
Eyes	25	6.22	10	2.50	< 0.05
Diabetes mellitus	36	8.96	24	6.00	> 0.05
Hypotension	12	2.99	10	2.50	> 0.05
Heart	27	6.72	16	4.00	> 0.05
Lung	11	2.74	6	1.50	> 0.05
Pancreas, thyroid, adrenal gland	10	2.49	8	2.00	> 0.05
Nervous system	35	8.71	32	8.00	> 0.05

The results of the analysis of the disease pattern of the residents in the two groups in Table 4 show that most of the diseases surveyed in this study in the TK group accounted for a statistically significant higher percentage (p < 0.05) compared with the ST group. This shows that people's health risks due to dioxin exposure around Da Nang airport were present and related to AO/dioxin residues.

Dioxin exposure in the TK group increased the incidence of diseases: hypertension, stomach, joints, ENT, liver-gallbladder, kidney-urinary system, and eyes diseases (33.58%, 23.88%, 40.3%, 11.19%, 6.47%, 7.21%, 6.22%, respectively), which was statistically significant (p < 0.05) from 1.8 times to 7.5 times higher than in the ST group. Diseases such as diabetes, and heart and lung diseases in the TK group (8.96%, 6.72%, and 2.74%, respectively) were also 1.2 times to 1.8 times higher than that of ST group, but they did not reach statistical significance (p > 0.05). In particular, in the TK group, the rates of 33.58% hypertension and 8.96% diabetes mellitus were higher than the general rates of 19.00% and 6.00, respectively of Vietnamese people (Bui et al. 2016).

Disease pattern of subjects in the research location by age

Table 5

Disease pattern in the age groups 45–69 and 18–44
Diseases	TK group (n = 402)				ST group (n = 400)				p
Diseases	45–69 years of age (n = 320)	Rate (%)	18–44 years of age (n = 82)	Rate (%)	45–69 years of age (n = 275)	Rate (%)	18–44 years of age (n = 125)	Rate (%)	p
Hypertension	131	40.94	4	4.88	72	26.18	4	3.20	< 0.05
Stomach	83	25.9	13	15.85	40	14.55	14	11.20	< 0.05
Joints	148	46.25	14	17.07	72	26.18	7	5.60	< 0.05
ENT	36	11.25	9	10.98	5	1.82	1	0.80	< 0.05
Liver and gallbladder	24	7.50	2	2.44	9	3.27	4	3.20	> 0.05
Kidney, urinary system	28	8.75	1	1.22	2	0.73	1	0.80	< 0.05
Eyes	21	6.56	4	4.88	8	2.91	2	1.60	< 0.05
Diabetes mellitus	35	10.94	1	1.22	23	8.36	1	0.80	< 0.05
Hypotension	4	1.25	8	9.76	7	2.55	3	2.40	> 0.05
Heart	26	8.13	1	1.22	14	5.09	2	1.60	> 0.05
Lung	8	2.50	3	3.66	6	2.18	0	0.00	> 0.05
Pancreas, thyroid, adrenal glands	9	2.81	1	1.22	4	1.45	4	3.20	> 0.05
Nervous system	33	10.31	2	2.44	24	8.73	8	6.40	> 0.05

People with diseases surveyed in this study concentrated in the age group 45–69 in both TK and ST groups. People aged 45–69 in the TK group had a 1.1 to 12 times higher prevalence of diseases in Table 5 than the ST group except for hypotension. People aged 18–44 in the TK group had statistically significantly higher rates of diseases: hypertension, stomach, joints, ENT, eye, and diabetes (p < 0.05) from 1.4 times to 13.7 times compared with the ST group. This indicates that there are many health risks for all residents living near the areas where AO/dioxin was stored in the Da Nang airport.

Disease pattern of subjects in the research location by sex

Table 6

Comparison of disease rates between men and women aged 18–69
Diseases	TK group (n = 402)				ST group (n = 400)				p
Diseases	Men (n = 120)	Rate (%)	Women (n = 282)	Rate (%)	Men (n = 130)	Rate (%)	Women (n = 270)	Rate (%)	p
Hypertension	49	40.83	86	30.50	27	20.77	49	18.15	<0.05
Stomach	19	15.83	76	26.95	11	8.46	43	15.93	< 0.05
Joints	38	31.67	124	43.97	15	11.54	64	23.70	< 0.05
ENT	9	7.50	36	12.77	4	3.08	2	0.74	< 0.05
Liver and gallbladder	10	8.33	16	5.67	3	2.31	10	3.70	< 0.05
Kidney, urinary system	12	10.00	16	5.67	0	0	3	1.11	< 0.05
Eyes	11	9.17	14	4.96	4	3.08	6	2.22	< 0.05
Diabetes mellitus	7	5.83	29	10.28	11	8.46	13	4.81	< 0.05
Hypotension	2	1.67	10	3.55	2	1.54	8	2.96	> 0.05
Heart	12	10.00	15	5.32	5	3.85	11	4.07	<0.05
Lung	9	7.50	2	0.71	4	3.08	2	0.74	> 0.05
Pancreas, thyroid, adrenal glands	3	2.50	7	2.48	2	1.54	6	2.22	> 0.05
Nervous system	3	2.50	32	11.35	6	4.62	26	9.63	> 0.05

The results of the analysis of disease patterns by sex in Table 6 show that the disease pattern depended on sex. Most of the diseases surveyed in this study in both sexes of the TK group accounted for a statistically significant higher rate (p < 0.05) than the ST group from 1.1 times to 17.3 times for women and from 1.1 times to 3.6 times for men. Men tended to have diseases: hypertension, and lung and eye diseases more than women. In contrast, women tended to have diseases of the stomach, joints, and nervous system at a higher rate than men.

The disease pattern of people in the TK group residing in areas at high risk of dioxin exposure had changed compared with the ST group residing far from the airport. The rate of diseases: ear-nose-throat, liver-gallbladder, kidney-urinary system, diabetes, and heart disease in the TK group was higher than that of the ST group.

Disease rates between men and women aged 45–69

Table 7

Comparison of disease rates between men and women in the 45–69 age group
Diseases	TK group (n = 320)				ST group (n = 285)				p
Diseases	Men (n = 100)	Rate (%)	Women (n = 220)	Rate (%)	Men (n = 93)	Rate (%)	Women (n = 182)	Rate (%)	p
Hypertension	47	47.00	84	38.18	25	26.88	47	25.82	< 0.05
Stomach	17	17.00	65	29.55	8	8.60	32	17.58	< 0.05
Joints	34	34.00	114	51.82	13	13.98	59	32.42	< 0.05
ENT	7	7.00	29	13.18	3	3.23	2	1.10	> 0.05
Liver and gallbladder	9	9.00	15	6.82	1	1.08	8	4.40	< 0.05
Kidney, urinary system	12	12.00	15	6.82	0	0	2	1.10	< 0.05
Eyes	9	9.00	12	5.45	4	4.30	4	2.20	< 0.05
Diabetes mellitus	7	7.00	28	12.73	10	10.75	13	7.14	> 0.05
Hypotension	1	1.00	3	1.36	1	1.08	6	3.30	> 0.05
Heart	11	11.00	15	6.82	4	4.30	10	5.49	> 0.05
Lung	8	8.00	0	0.00	4	4.30	2	1.10	> 0.05
Pancreas, thyroid, adrenal glands	2	2.00	7	3.18	1	1.08	3	1.65	> 0.05
Nervous system	3	3.00	30	13.64	5	5.38	19	10.44	> 0.05

Table 7 shows that people aged 45–69 in both TK and ST groups had higher rates of hypertension and eye diseases in men than in women. In contrast, diseases such as stomach, joints, and pancreas-thyroid-adrenal in women account for a higher rate. In the TK group, both men and women had a prevalence of most diseases that was 1.2 to 12 times higher than that of the ST group.

Disease rates between men and women aged 18–44

Table 8

Comparison of disease rates between men and women in the age group 18–44
Diseases	TK group (n = 82)				ST group (n = 125)				p
Diseases	Men (n = 20)	Rate (%)	Women (n = 62)	Rate (%)	Men (n = 37)	Rate (%)	Women (n = 88)	Rate (%)	p
Hypertension	2	10.00	2	3.23	2	5.41	2	2.27	< 0.05
Stomach	2	10.00	11	17.74	3	8.11	11	12.50	< 0.05
Joints	4	20.00	10	16.13	2	5.41	5	5.68	< 0.05
ENT	2	10.00	7	11.29	1	2.70	0	0	< 0.05
Liver and gallbladder	1	5.00	1	1.61	2	5.41	2	2.27	> 0.05
Kidney, urinary system	0	0	1	1.61	0	0	1	1.14	> 0.05
Eyes	2	10.00	2	3.23	0	0	2	2.27	> 0.05
Diabetes mellitus	0	0	1	1.61	1	2.70	0	0	> 0.05
Hypotension	1	5.00	7	11.29	1	2.70	2	2.27	< 0.05
Heart	1	5.00	0	0	1	2.70	1	1.14	> 0.05
Lung	1	5.00	2	3.23	0	0	0	0	> 0.05
Pancreas, thyroid, adrenal glands	1	5.00	0	0	1	2.70	3	3.41	> 0.05
Nervous system	0	0	2	3.23	1	2.70	7	7.95	> 0.05

Table 8 shows that among people aged 18–44 in both TK and ST groups, men tended to have diseases: hypertension, liver-gallbladder, and heart diseases more than women. In contrast, women had higher rates of diseases such as stomach, kidney-urinary system, and nervous system than men. In the TK group, both men and women had higher rates of diseases such as hypertension, stomach, joint, ear-nose-throat, eye, hypotension, and lung diseases than those in the ST group from 1.2 times to 5.0 times.

Rates of women with menstrual disorders and risks of birth defects

Table 9

Rates of women with menstrual disorders and risks of birth defects
Menstrual disorders and risks of birth defects		TK group (aged 18–69, n = 282)				ST group (aged 18–69, n = 270)				p
		Aged 18–44 (n = 62)		Aged 45–69 (n = 220)		Aged 18–44 (n = 88)		Aged 45–69 (n = 182)
		Rate (%)	Number	Rate (%)	Number	Rate (%)	Number	Rate (%)	Number
Menstrual disorders		9.68	6	11.82	26	14.77	13	9.89	18	> 0.05
Risks	Delayed physical development	0	0	0.45	1	0	0	0	0
Risks	Mental retardation	0	0	1.82	4	0	0	2.20	4

Dioxin is known to menstrual disorders, changes in the average age of puberty, causes birth defects and reproductive complications in women (Institute of Medicine 2014). The results of Table 9 show that there was no statistically significant difference (p > 0.05) in the proportion of women with menstrual disorders between the TK group and the ST group in both ages. Women aged 45–69 in the TK group had menstrual disorders with a rate of 11.82%, which was higher than that of the ST group (9.89%). But in the age group of 18–44, the ST group had a higher rate of menstrual disorders (14.77%) than the TK group (9.68%).

Table 9 also shows that the TK group had two types of risks: delayed physical development (0.45%) and mental retardation (1.82%) and both belonged to women aged 45–69 but there was no statistically significant difference between the two groups.

Rates of reproductive complications

Table 10

Rates of reproductive complications
Complications	TK group (n = 282)				ST group (n = 270)					p
	Aged 18–44 (n = 62)		Aged 45–69 (n = 220)		Aged 18–44 (n = 88)		Aged 45–69 (n = 182)
	Rate (%)	Number	Rate (%)	Number	Rate (%)	Number	Rate (%)	Number
Premature birth	6.45	4	3.64	8	0	0	3		1.65	< 0.05
Hydatidiform mole	0	0	0	0	0	0	0		0	> 0.05
Hydatidiform mole with complications	0	0	0	0	0	0	0		0	> 0.05
Dead malformed birth	0	0	0.45	1	0	0	0		0	> 0.05
Living malformed birth	0	0	1.36	3	1	1.14	0		0	> 0.05
Stillbirth	0	0	0.45	1	0	0	1		0	> 0.05
Postnatal death	0	0	0.45	1	0	0	0		0	> 0.05

As the results of Table 9 show that there was no difference in the mean age of puberty as well as the prevalence of menstrual disorders in women between the 2 groups of TK and ST. But the results of Table 10 show that there was a clear difference in the rate of reproductive complications between the two groups. In the TK group, women encountered 5 types of reproductive complications more than in the ST group, in which the factor of preterm birth reached statistical significance (p < 0.05) compared with the ST group.

The rates of premature birth, dead malformed birth, living malformed birth, and postnatal death in the TK group (3.64%, 0.45%, 1.36%, and 0.45%, respectively) were higher than in the ST group (1.65%, 0%, 0%, and 0%, respectively). Health risks were evident for women in the TK group between the ages of 45–69, as their longer residence time around the hot spot means they also had a longer exposure to AO/dioxin and thus experienced all 5 types of complications, while women aged 18–44 of this group only encountered 1 type of complications, which was preterm birth. In the same age group of 45–69, the ST group lived far from the airport, so they only encountered 2 types of complications: premature birth and stillbirth. Especially, the rate of premature birth in the TK group (6.45% and 3.64%) was significantly higher (p < 0.05) than in the ST group (0% and 1.65%).

The distribution of people's age and residence time of the two groups were similar, consistent with the selection criteria and priority survey of subjects with a long, stable residence time in two areas TK and ST in order to eliminate the confounding factor of time. Residents aged 45–69 had a high percentage in both groups (TK group: 79.60% and ST group: 68.75%) (Table 1). The percentage of residents living for more than 15 years was the majority (89.30% in TK group and 90.75% in ST group) (Table 1). As such, these people had settled down, had long-term exposure to AO/dioxin, and bore many health risks due to daily exposure to the surroundings of the hot spot (Hatfield Consultants and Office of the National Steering Committee 2009), local high-risk air and food use (Sau et al. 2021; Tuyet-Hanh et al. 2015).

In this study, women were prioritized for interviews in both groups (Table 1), so they accounted for the majority (TK group: 70.15%, ST group: 67.50%). Because women were subjects of reproductive health and could answer extensively about diseases and illnesses of family members. Women also often did housework, so they had more time to live and work at home in the TK group and ST group regions more often and for a long time. Women also worked in jobs with low exposure to toxic elements related to industrial and residential activities. Women were also less likely to use alcohol, beer, and tobacco than men. Thus, this study limited confounding factors and excluded health risks, not due to dioxin exposure.

Exposure to risk factors for diseases such as foodstuffs, waste treatment, waste incineration, pesticides, chemical fertilizers, cement, metallurgy, rubber and wood processing, etc. may also increase the risks of diseases (Minh et al. 2019). Table 2 shows that the proportion of people exposed to toxic factors not related to dioxin in both TK and ST groups was very low, only from 0–0.75%, therefore, in the assessment of this study, interference from industrial and residential activities can be excluded.

The proportion of people who had been directly and indirectly exposed to AO/dioxin during the war and stored in Da Nang airport of the TK group was 3.48% and 9.45%, respectively, which was higher than that of the ST group (0% and 1.75% respectively) (Table 2). But the greatest health risk and high risk of AO/dioxin exposure were for people in the TK group due to their frequent and long-term residence around former hot spot locations. This was the main cause of the difference in disease patterns between the TK group and the ST group.

There were still about 13.7% of households in the TK group that self-increasing, growing vegetables, raising fish and poultry around the airport and using it as food, which was the cause of food poisoning with the rate of 13.7% and higher than that of the ST group (Table 3). This shows that the risk of AO/dioxin exposure and health risks in the TK group was present and people in the TK group suffered from many diseases at a higher rate than in the ST group. This was also consistent with previous results (Wittsiepe et al. 2007; Todaka et al. 2010).

Previous studies have shown that disease properties are related to sex and age (Choi et al. 2017; Nordström et al. 2016). This study investigated and compared the disease pattern according to age and sex of both TK and ST groups, focusing on the diseases related to a number of systems and organs in the body that are sensitive to AO/dioxin. Dioxin exposure has damaged a number of organ systems in the human body such as the liver, nervous system, immune system, hormones, respiratory system, lungs, etc. (Center for Health Environment and Justice 1999).

The results in Tables 4, 5, 6, and 7 indicated that dioxin exposure by residents near the hot spot increased the prevalence of multiple diseases. The prevalence of diseases in the whole group aged 18–69 was 1.1 to 9.6 times higher than that of the ST group (Table 4); those aged 45–69 was 1.1 to 12 times higher than the ST group (Table 5); Between the ages of 18–44, the prevalence of hypertension, stomach, joints, ear-nose-throat, kidney-urinary system, eyes, diabetes, and hypotension was 1.4 to 13.7 times higher than ST group.

The disease pattern depends on sex, but dioxin exposure due to residence near the hot spot was still the main factor creating the difference in disease pattern between the two groups of TK and ST (Table 6). Health risks and disease risks were higher for both sexes of the TK group. Women in the TK group had a higher rate of all diseases than the ST group from 1.1 to 17.3 times and for men, it was 1.1 to 3.6 times higher (except for diabetes and diseases of the nervous system). Compared with the ST group by two ages in Tables 7 and 8, it was found that the prevalence of most diseases in men in the TK group was from 1.7 times to 8.4 times higher in the age group 45–69 and higher from 1.2 times to 3.7 times in the age group of 18–44; and these rates in women of the TK group were from 1.2 times to 12 times higher and from 1.4 times to 5 times higher in the two age groups, respectively.

The dioxin concentrations in breast milk collecting in 2008 and 2009 from mothers of the TK group were high and ranged from 12.8 to 14.3 pg TEQ/g lipid (Tai et al. 2011). Dioxin exposure from the milk of mothers living near the Da Nang hot spot in the TK group had a negative impact on the physical, nervous system, cognitive, language, autistic traits, and motor development of the children (Nishijo et al. 2012; Anh et al. 2014; Nishijo et al. 2014; Tran et al. 2016).

The results of this study on the effects of AO/dioxin on reproductive health also noted the state of reproductive complications in women as well as the risk of birth defects in young children (Institute of Medicine, 2014). However, no difference was found in the mean age of puberty and the proportion of women with menstrual disorders. Table 10 shows that women of the TK group residing around Da Nang airport were at risk of a higher number of reproductive complications and at a higher rate than the ST group residing far from the airport. In the TK group, women aged 45–69 had a longer exposure to AO/dioxin than women aged 18–44, so they suffered many reproductive complications such as dead malformed birth, living malformed birth, stillbirth, and postnatal death. And especially, only between the ages of 45–69 had children born with delayed physical development and mental retardation (Nishijo et al. 2015; Pham et al. 2015; Tai et al.2016).

The TK group was exposed to many health risks due to their residence near areas that were formerly AO/dioxin hot spots within Da Nang airport. The diseases recommended by WHO related to AO/dioxin exposure in the TK group accounted for a higher proportion than the ST group. The prevalence of diseases of the people in the two groups depended on the residence time, sex and age. But the main factor determining the difference in disease pattern was the local AO/dioxin exposure.

Exposure to AO/dioxin during 50 years remaining in Da Nang airport was one of the causes affecting the disease pattern of people in TK group as well as increasing the incidence of some diseases and some reproductive complications.

Acknowledgements We gratefully thank the Joint Vietnam-Russia Tropical Science and Technology Research Center for their assistance and encouragement in carrying out this study.

Funding This work was supported by the Joint Vietnam-Russia Tropical Science and Technology Research Center under grant number M-3.3.

Authors’ contributions Trinh Khac Sau and Dinh Viet Hung designed the study and organized the data collection. Trinh Khac Sau, Quan Van Le, and Le Van Quang conducted the survey and/or the data analyses. Trinh Khac Sau, Dinh Viet Hung, and Quan Van Le drafted the manuscript. All the authors made critical revisions and agreed on the final version of the manuscript. Trinh Khac Sau and Dinh Viet Hung reviewed the final manuscript and approved it for submission.

Compliance with ethical standards

Conflict of interest The author(s) declare no potential conflicts of interest concerning the research, authorship and/or publication of this article.

Ethical approval This study has been approved by Vietnam-Russia Tropical Center Ethics Committee (operation number: IRB-VN02017 issued by Ministry of Health) with code number 18/2020/VREC. All participants are completely voluntary and may withdraw from the study at any time. The information in the survey is kept confidential.

Consent to participate All authors have read, approved and accept responsibility for the manuscript.

Consent for publication We consider Environmental Monitoring and Assessment to be an appropriate journal for the publication of this manuscript. We confirm that this manuscript has not been published before and is not under consideration for publication in another journal

Code availability Not applicable

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No competing interests reported.

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Investigation on ratios of some common diseases and health risks relating to dioxin exposure in Da Nang, Vietnam

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