Ye Zhenzhen was unmoved, and still insisted on her opinion, "I still think it's good to be on the top of the food chain, the example you just mentioned is just an example, and it's because of man-made pollution." ”

Nan Zhiqiao sighed: "Yes, many things are caused by human beings' own mistakes. ”

"Senior Nan, do you think this strange illness in Nanwan Town will be caused by environmental pollution?"

"It's hard for me to make a judgment until I investigate it, but there are two most likely scenarios: environmental pollution or food poisoning, either way, you have to find out the cause, otherwise the strange disease will keep appearing. ”

If it is environmental pollution, then the situation may be the same as the situation in Minamata City, Japan, and if it is food poisoning, there is a precedent.

In 1971, Iraq imported a consignment of wheat grains from the United States and Mexico that contained methylmercury.

The poisoned wheat grains were sold to the local population of Iraq, and after the residents ate them, they developed symptoms of poisoning, and more than 600 people died as a result.

Why does imported wheat contain methylmercury?

Later, people found out the ins and outs of the whole thing, and it turned out that this batch of wheat grains was not for people to eat.

A biological company had developed a fungicide containing methylmercury, and the wheat grains had been soaked in the fungicide, and the bags were printed with the words "This is an experiment, not edible" and a skull and two crossbones together with a poison symbol.

When the grains arrived in Iraq, for some unknown reason, the distributors did not know that the grains were inedible and sold them to the local population as edible grains.

When the poisoned wheat caused the death of a large number of residents, people did not realize that it was the problem of the wheat grains and continued to eat them. More than two months had passed since researchers finally discovered the source of the poisoning, during which time more than 600 people died.

Thinking of these things, Zhen Zhen couldn't help but worry about the strange illness incident in South Bay Town.

——

After the seafood dinner, Nan Zhiqiao and Zhen Zhen did not go back to the hotel, but bought some live seafood in the seafood street, as well as packed Nanwan Town Push Wave Fish, and went to the Lianhai City Center for Disease Control and Prevention.

At half past eight in the evening, the lights were still on in the CDC laboratory building.

Nan Zhiqiao called Liang Lei, and Liang Lei waited in front of the experimental building early in the morning to collect the sample.

When the three met, Nan Zhiqiao handed Liang Lei the wave fish he brought back from the hotel and told him his plans.

For this batch of wave-pushing fish, the mercury content in the fish was mainly tested, which can indirectly indicate whether the sea near Nanwan Town is contaminated with metallic mercury.

Liang Lei also reported to Nan Zhiqiao about the sampling situation in the hospital in the afternoon, at present, there are twelve strange patients who come to the city hospital from Nanwan Town for treatment, in addition to the two little sisters who have died, there are still ten people hospitalized in the hospital, as for whether there are more cases in the hospital in Nanwan Town or Guanhai County, I don't know.

The blood, urine, and hair samples of the 10 patients with strange diseases in the urban hospital were all collected and sent for testing, and the results will be available tomorrow morning.

——

After a night's rest in the hotel, early the next morning, according to the previous arrangement, Nan Zhiqiao will attend a training meeting to train the personnel of the local city, county and district disease control system on epidemiological field investigation.

The training content has already been sorted out into PPT files, the morning training meeting, Nan Zhiqiao spoke for more than two hours, after that, the on-site trainers raised a lot of practical questions, Nan Zhiqiao patiently answered one by one.

By the time the training session ended, it was close to noon.

As soon as the meeting ended, Liang Lei hurriedly showed the test results to Nan Zhiqiao.

Specimens from patients with strange diseases are tested in three ways: urine mercury, mercury, and blood mercury.

The first indicator, urine mercury, mainly reflects the patient's recent mercury intake. In China, the urinary mercury content in the normal human body is capped at 50 milligrams per liter, and the urine mercury content of this group of patients in Nanwan Town is more than 400 milligrams per liter, and some are even as high as 1000 milligrams per liter.

Minami no Qiao thought of the previous situation of Minamata disease in Japan, within five months of the onset of the patient's illness, the patient's urine mercury excretion peaked, the daily amount of 40 to 1200 micrograms, while the control group was less than 16 micrograms per day, and in cases of more than one year, the urine mercury became less, and the daily mercury excretion fell to less than 30 micrograms, and the initial urine mercury was diagnostic.

Based on previous data and experience, Nan Zhiqiao judged that the patient in Nanwan Town was in the early stage of mercury poisoning, and the poisoning time was less than one year.

The second indicator, mercury, mainly reflects the level of mercury ingested by the human body in the past, which can trace the history of mercury contamination in the human body. The upper limit of mercury levels in normal human bodies is 10 micrograms per gram, and the minimum mercury levels that can cause neurological disorders in adults are 50 to 125 micrograms per gram, while the mercury levels of patients in Nanwan Town are around 500 micrograms per gram, which is seriously excessive and close to the lethal level.

The third indicator - blood mercury, when the whole blood mercury content is 20 micrograms per 100 milliliters, there will be no symptoms of poisoning, when 20 to 50 micrograms per 100 milliliters, symptoms begin to appear, and when it exceeds 100 micrograms per 100 milliliters, there will be obvious symptoms of poisoning. The blood mercury level of the patient in Nam Wan Town was around 110 micrograms per 100 millilitres, which is also close to lethal levels.

Nan Zhiqiao frowned slightly, he didn't expect the patient's condition to be more serious than he thought.

The strange disease in the town of South Bay can be confirmed as mercury poisoning.

But what is the source of poisoning?

Liang Lei took out the live seafood report sent by Nan Zhiqiao for inspection yesterday.

Surprisingly, the mercury levels of the wave-pushing fish brought from the town of South Bay were within the normal range.

Could it be that the situation in Nanwan Town is different from that in Minamata City, Japan, because of environmental pollution, which caused the accumulation of methylmercury in fish and caused illness among local residents?

In the conference center on the top floor of the main building of the CDC, the participants in the training have dispersed, leaving only Nan Zhiqiao, Liang Lei and Ye Zhenzhen.

Standing beside Nan Zhiqiao, Zhen Zhen took the test report in Nan Zhiqiao's hand, and after reading it, she said, "It can be determined that it is mercury poisoning." ”

"Teacher Nan, what should I do now?" Liang Lei looked at Nan Zhiqiao, and then asked: "After feeding back the results to the hospital, what we CDC have to do is an on-site investigation, right?"

"Yes, the test results inform the hospital, they will carry out mercury removal treatment according to the plan, and what we need to do is to find out the scope and severity of this methylmercury poisoning incident, as well as the source of the poisoning. ”

Liang Lei thought for a moment and said hesitantly: "The patients of this methylmercury poisoning incident are all residents of Nanwan Town, if you want to investigate the scope of the incident, should the entire Nanwan Town be investigated? There are more than 20,000 permanent residents there." ”

More than 20,000 people, if you check them one by one, it is indeed a big project.

Nan Zhiqiao gave advice: "Start with the cases that have already occurred, and investigate the living environment and contact groups of patients before they are admitted to the hospital, and there will be clues to the source of poisoning." The focus of the survey is on the people who live in the same environment as the patient, and samples are taken for urinary mercury, mercury hair and blood mercury. ”

The scope of the investigation was narrowed down by Nan Zhiqiao, and the work became focused.