Considering DDT was banned in 1972... any suits who were alive during its production and would be behind the decision to dump all of this stuff out into the sea, assuming a median age of 40, would be 89 years old today.
TLDR: Those responsible are probably all dead now.
DDT was not banned in the US in 1972. The use of DDT in agricultural applications was banned in the US in 1972. As far as I know, it's still legal to manufacture and still legal to use for mosquito control.
> The United States banned the use of DDT in 1972, but some countries still use the chemical. DDT has also been used in the past for the treatment of lice. It is still in use outside the United States for the control of mosquitoes that spread malaria.
EPA says its use was discontinued (read: cancelled)
> In 1972, EPA issued a cancellation order for DDT based on its adverse environmental effects, such as those to wildlife, as well as its potential human health risks.
"Some uses of DDT continued under the public health exemption. For example, in June 1979, the California Department of Health Services was permitted to use DDT to suppress flea vectors of bubonic plague.[52] DDT continued to be produced in the United States for foreign markets until 1985, when over 300 tons were exported"
The above CDC and EPA citations were clearly over-generalizations, disregarding the public health exemption, since DDT was used legally in the US in 1979.
I'm not sure how late it was specifically used in the US for mosquito control vs. flea control, but as far as I know, the public health exemption still exists (though, I suspect it's nearly impossible to get an EPA permit today). I could very well be wrong, and the public health exemption may no longer exist.
In any case, the claim that it must not have been manufactured legally in the US after 1972 is false. The 1972 ban is less comprehensive than commonly believed.
TLDR: Those responsible are probably all dead now.