The proposed site for David Beckham’s Major League Soccer stadium in Miami is far more toxic than previously expected, according to environmental analysis.

The Miami Herald said the analysis found arsenic contamination reaching more than twice the legal limit, and surface-level soil samples containing hazardous debris at the Melreese golf course site, where people have played golf for more than 50 years.

The 131-acre site is being considered for a sprawling billion-dollar (£827 million) commercial and stadium complex that would be home ground for Beckham’s MLS team, Inter Miami.

According to the consultant’s report, the pollution under the grass on the golf course was caused by contaminated ash from a municipal incinerator shut down long ago.

In some spots, the contamination is near the surface, as shallow as 6in deep.

The worse-than-expected findings were reported to city commissioners.

“This is the largest contaminated park in the city’s portfolio,” said commission chairman Ken Russell. “This is a concern.”

Environmental firm EE&G, hired by Inter Miami, took more than 140 soil samples in recent months. Apart from the arsenic, it found barium and lead levels above legal limits.

“The debris included fragments of tile, metal and glass, mixed with fine-grain sands, which often exhibited a rusty colour,” EE&G found.

“Intermittent wood fragments were encountered along with concrete and other non-native materials, but not evidence of municipal garbage.”

Miami mayor Francis Suarez said he was glad the site had been tested, and said the city has chosen another consulting firm, AECOM, to conduct its own analysis of the findings. The firm also will be paid by Inter Miami.

“Basically, the site has significantly more contamination than what is commercially reasonable,” Mr Suarez said.

The findings could increase clean-up costs to 50 million dollars (£41 million) at the site, team officials told Mr Suarez. The Herald reported that it was not clear whether the added cost would make the plans for a stadium and commercial complex unfeasible. Inter Miami said it would not seek city money to pay for the clean-up.

The environmental concerns come as the city negotiates a 99-year lease for a commercial complex that would allow a 25,000-seat stadium, office park, shopping centre and football fields on the roof of a parking structure.

Inter Miami’s lawyers are expecting to propose a lease on September 12, and the terms would need the approval of four of five commissioners.