Bullying against foreigner workers is depicted objectively. Kazuo endured it, but the superior did not end bullying. Here are long lasting problems.
And in the story, another problem of leakage of industrial waste's treatment water is suspected to have committed by Kazuo's employer.
Is it connectable to Kazuo's death?

Did Kazuo anticipated his own death?

Lament of his mother and his colleagues were also depicted.