The fracking industry must be compelled to provide far more detailed information to regulators if the public is to be accurately informed of any risks to the environment, advocacy groups say.

A report by the Environmental Protection Agency (EPA) last month found that hydraulic fracturing for oil and gas can lead, and has led, to the contamination of drinking water. It was the first time the federal government had admitted such a link.

The study, based on “data sources available to the agency”, found levels of any contamination to be small compared to the number of wells across the country, the EPA said.

But Gretchen Goldman, a lead analyst at the Center for Science and Democracy at the Union for Concerned Scientists, told the Guardian that the EPA’s study – which is now open for comment – was nothing “more than a literature review” and called for the industry to be required to divulge greater data.

Goldman says the EPA backed down from its initial promise to undertake prospective studies, which would have involved following a well site and testing its waters before, during and after fracking activities had begun. Such a study would have shed objective light on the fracking process and pushed scientific knowledge forward, she says.

Information shared by the industry for the report was very often done on a voluntary basis, the authors reveal, and even when companies were forced to share information through state regulations, they were still allowed to withhold details deemed crucial to their business.

One of the most notable elements of fracking that continues to be shrouded in secrecy, for instance, is the identity and mixture of chemicals that are injected into the ground through wells, together with water, at high intensity to fracture underground rocks and release oil or gas.

The chemical composition of such injections appears to vary from company to company and well to well.

Even if the EPA was able to compile a list of 1,076 chemicals used in the fracking process, the list is incomplete, with businesses involved in fracking able to cite some components as amounting to confidential business information, and therefore not subject to release to the public, the report indicates.