The owner of a north Minneapolis metal scrap yard disputed Saturday that air measurements taken by state regulators near the yard represent a health risk for heavy metals and said that it doesn't yet know what air-quality permit requirements it is alleged to have violated.

Northern Metal Recycling released a highly technical analysis responding to a Minnesota Pollution Control Agency statement on Wednesday saying that levels of the metals in the air near the yard are a cause for concern.

The company said the MPCA's analysis overstates the risk from nickel and chromium measured by state air monitors across the street from the yard where a large enclosed shredder pulverizes scrap metal and further processes it for use in steel and other mills. The company also charged that the agency has insufficient data for cobalt measurements.

Northern Metal also disputed the Minnesota Department of Health's contention that the readings for these metals, lead and air particles have the potential for long-term harm, especially for workers in the area. It said lead levels measured fall well below thresholds set by OSHA for shift and 24-hour exposure.

MPCA did not allege that the metals measured violated air-quality standards, but noted that poor air quality can prompt health issues such as respiratory irritation, lung damage and cancer. Lead can cause cardiovascular issues in adults and developmental problems for children. The agency said that the surrounding residential area already has more children with higher lead levels in their blood, but an agency scientist said it's unlikely lead particles would travel as far as those neighborhoods.

The company statement didn't specifically address the cause of continuing violations of air quality standards for high levels of microscopic particles measured by air monitors. MPCA this week also alleged "potentially serious" permit violations that it said it recently learned about. It would say only that the issues involve operations outside the controversial shredder that began operating in 2009 at the three-square-block scrap yard.

But the company did hint in its statement that its metals recovery plant may be a source of state scrutiny. That building further processes nonferrous scrap, including "fluff" captured at the shredder. The company said that the building was discussed in an environmental work sheet, was visited once by agency staff, and has been available for inspection. It said that the building is classified as an "insignificant source" for permit purposes and was discussed as a potential source of particles last year.

MPCA reacted to the company's response with this statement: "The MPCA is confident that our monitoring data shows a serious problem and provides strong indications of where the problem is coming from. We will continue our investigation and go wherever the evidence leads us."

Steve Brandt • 612-673-4438 Twitter: @brandtmpls