Chinese authorities have launched a nationwide probe into contaminated milk powder after government health authorities said dozens of babies fed with the milk were diagnosed with kidney stones, and one infant died.

An initial probe found a chemical used for plastics called tripolycyanamide, which can cause kidney stones, in milk powder produced by Sanlu Group, a state-owned dairy products company based in northern China’s Hebei Province.

Sanlu confirmed an internal company investigation found its milk powder produced between March and August 5 was contaminated by the chemical. Sales of the product were halted August 6, the company said, although the public recall announcement was delayed for more than a month.

Sanlu is defending itself, saying the contamination was caused by milk suppliers rather than the company’s production procedure.

Su Changsheng, the company’s brand manager, told Caijing that “Sanlu’s milk powder is made with fresh milk. If the milk contains tripolycyanamide, the milk powder also would contain it.”

According to Su, the company does not test for tripolycyanamide because China has no national standards for testing milk products for the chemical.

Su said dairies may be tempted to add tripolycyanamide to boost nitrogen levels because tests for nitrogen are conducted to determine protein levels in milk.

Sanlu is now registering customers and has promised to compensate those who bought contaminated milk powder.

The company said sales were halted on August 6, and 700 tons of the baby milk powder has been recalled. However, Caijing learned from some customers that the product was still on market shelves as recently as August 9, and some sellers said they heard nothing from Sanlu before receiving a recall notice September 11.

The Ministry of Health linked Sanlu milk powder to kidney stones in 59 babies and the death of one baby in Gansu Province. Similar cases have been reported in the Ningxia Hui Autonomous Region as well as Shaanxi, Jiangsu, Shandong, Anhui and Hunan provinces.