The initial cases were found in three individuals from one family. Their initial symptoms were sore throat, diarrhea, bloating, rashes with itching, poor appetite, nausea, and vomiting. Their biological samples showed arsenic levels above local reference-levels including arsenic concentrations in the hair (normal <5.0 μg/g) and urine (normal <0.2 mg/L). Around August 23, 2018, a heap of slags had appeared on a hill near their village, and a continuous heavy rainfall occurred around October 13 when the slags were stacked, and a part of the slags seemed to have been washed into the public well and a karst cave underside. The underground water flowed through the cave and the water in the public well were likely contaminated after this rainfall. The three individuals reported using public well water to wash clothes, food, and cook meals. From reports from the local government and local CDC, the slags contained 3.66×103 mg/kg of arsenic, and the soil contained 1.86–2.08 mg/kg of arsenic. According to information above, their poisoning was likely related to the arsenic-containing slags, and the public well water may have been contaminated and poisoned these people.
To control the contamination and find potential cases, NIOHP and HPTIOD formed a joint investigation team (JIT) to investigate the cases and created a specific case definition. Suspected cases were defined as residents living in Xiongxin Village, Yongan County, Hunan Province since Octomber 2018 who had at least one of the following symptoms with unknown specific-causes: gastrointestinal problems including nausea, vomiting, and diarrhea; neurological symptoms including dizziness, weakness, and insomnia; and respiratory system problems including throat pain. Confirmed cases were defined as suspected cases that had hair arsenic levels >5.0 μg/g or urinary arsenic levels >0.2 mg/L. On November 15, 7 suspected cases were found, and they were confirmed the next day because of the high arsenic in their hair or urine.
The 10 confirmed patients’ signs and symptoms all matched those of acute arsenic poisoning (details are presented in Table 1). These patients also all had sensory nerve conduction threshold decline or peripheral neurogenic damage of the limbs, either unilaterally or bilaterally. The ages of the patients were ranged from 8 years old to 48 years old, and the median age was 42 years old. There were 5 females and 5 males. The median date of symptom onset in the patients was October 21, 2018 (range: mid-October to December 11). The median date of diagnosis was November 16 (range: November 14 to 16). The median urine arsenic was 0.28 mg/L (range: 0.04 mg/L to 0.92 mg/L). The median hair arsenic was 20.2 μg/g (range: 3.5 μg/g to 35.6 μg/g). Their biological samples showed other heavy metals, although none of the metals were above toxic doses. None of the patients had direct contact with the slags; however, they all used the common public well water for domestic use excluding drinking.
Symptoms Number Percent (%) Diarrhea 6 60 Vomit 6 60 Fatigue 6 60 Dizziness 3 30 Sore throat 2 20 Hyperpigmentation 2 20 Feet and wrist drop 2 20 Insomnia 2 20 Head ache 1 10 Tongue numbness 1 10 Pain allergic in feet 1 10
Table 1. The signs and symptoms of the patients in arsenic poison accident of Hunan Province in 2018 (N=10).
The epidemiological investigation and field hygiene investigation was conducted in December 2018 to verify the source and the route of poison. First, the results showed that the level of arsenic in the water of a patient’s water container and the water exuded from the sealed public well was 192.4 times and 6.8 times of arsenic standard in drinking water, respectively. The water in the container was pumped from the public well and the public well had been sealed before the JIT arrived. A fish sample collected from a private pond near the public well tested high in arsenic levels as well. The detailed results are presented in Table 2. This information confirmed that the domestic water of patients and public well water were all polluted. Second, there was a ditch and an underground river between the area that the slags were stacked and the public well. The underground karst cave could be detected and the sound of water underground could be heard, but due to equipment limitations, no samples from the cave were collected. Third, the patients were all found to be living within a radius of 40 meters. The average distance between their houses and the public well was 67.5 meters (range: 50–100 meters), and the slags were no more than 200 meters from their houses. The height of the slags’ location was higher than the surrounding markers with an average height difference of 3.4 meters (range: 2–5 meters). Therefore, we inferred that the slags had likely flowed into the public well and the cave due to heavy rain.
Material Arsenic concentration (mg/L) Reference range (mg/L) Domestic water 9.62 0.05 Water exuded from public well 0.34 0.05 Fish meat 0.11 − Private well water − 0.05 Water from the ditch < 0.05 0.05
Table 2. The arsenic concentration in samples of the environment in the poison accident of Hunan Province in 2018.
In summary, patients often used the public well water for domestic purposes, and the patients’ collected water in their containers was found to be highly polluted. The public well water was likely contaminated by the slags, and the patients were likely poisoned when using the public well water for domestic purposes excluding drinking.