The Ministry of Environmental Protection has started an investigation into what caused about 500 students at a middle school in East China's Jiangsu province to come down with a range of illnesses. 

Last September, the school had relocated to a new facility, which was built on a site that had housed three chemical factories.

12 year-old Zeng is a student at Changzhou Foreign Languages School. After the school relocated to a new site, the pain started.  

Her classmate Jin had other symptoms.  A severe headache and a rash all over his face. And they weren't the only ones.

Within months, more than 600 students went to doctors.

Nearly 500 were diagnosed with various illnesses and conditions. Several had leukemia.  

Frightened parents started to deliver home-made food and water, doubting the safety of the school cafeteria.

Some of them point fingers at an excavation site only a street away from the school, where three chemical factories stood.

A senior staff member who had worked in the Changlong factory, the biggest of three, spoke on the condition of anonymity.  He said they used to produce highly toxic chemicals such as the pesticide methomyl.
 
This environmental report reveals that a great amount of pollutants were detected underground after the factories moved away.

and the level of some major pollutants like chlorobenzene [klɔːrəʊ'benziːn], are reportedly nearly 100 thousand times the safe limit.

In December 2014, the factory had been fined 160 million yuan for contamination.

So why was the school was allowed to be built less than 100 meters away?

Education authorities say the site passed inspection.

"The soil in the school site reached the standard after examination. From the assessment report, the site met the standards for building a school," said Ji Zhong, Deputy Dir. Gen., Changzhou Education Bureau.

But experts found big loopholes in the assessment.

"The assessment only measured conventional pollutants or heavy metals in the site's soil and water conditions, such as ammoniacal nitrogen and mercury. In fact, it did not take pesticide pollutants into consideration," said Professor Liu Yangsheng, Environmental Sciences & Engineering, Peking Univ..

The students' parents have hired a testing company to conduct further assessments.

where multiple pollutants were reportedly detected in the water, soil and even air near the school's new site.

An expert has weighed in on the case.

"The pollution was obvious, and as far as I'm concerned, the pollutants detected are similar to the chemical discharge from those factories. There could be some links," said Professor Pan Xiaochuan, School of Public Health, Peking University.

And while local authorities conduct further investigation, the danger remains.