US research NGO TEDX (The Endocrine Disruption Exchange) says analysis of the evidence that melamine exposure could have human health impacts beyond kidney function means research in this area should also focus on memory and learning.
Melamine is a high production volume substance used in a wide range of consumer products including some intended specifically for food contact. These include tableware, food utensils and food packaging.
The scientists say the evidence is sufficiently robust for systematic review of the hazards endpoints in three categories:
- neurology and behaviour; and
- anthropometric outcomes, which relate to body size and weight.
The evidence is most robust, they say, for systematic review of neurological and behavioural endpoints. They add that, if the systematic review were to suggest a relationship, there would already appear to be sufficient mechanistic research to support the the "biological plausibility" of effects of learning and memory.
The scientists identified 43 relevant studies, published in 2010 or later and covering a wide range of species and endpoints. Of these: 17 concerned reproduction; 16 neurology; 13 behaviour; and 20 anthropometric outcomes relating to body weight, body length and fetal growth.
TEDX's analysis, presented as a scoping review, has been accepted for publication in Toxicology Letters, a peer-reviewed journal. It was supported by funding from a group of NGOs including ChemSec, and produced in collaboration with the University of Colorado.
Melamine made news in 2008 when it was discovered to be the cause of illness and death among infants and children in China. Unscrupulous producers were adding the substance to powdered milk and baby formula to cheat quality tests based on protein content, as determined by nitrogen content. This led to urinary tract stones and kidney failure in affected individuals.
Following the scandal, the European Food Safety Authority (Efsa) lowered its tolerable daily intake (TDI) to 0.2mg per kg of body weight and the European Commission lowered the limit to 2.5mg per kg of food (mg/kg food) to align it with the new TDI.
In Europe the substance does not carry a mandatory classification, while according to the notifications provided by companies to Echa in REACH registrations no hazards have been classified.
In 2014, a Thai study suggested that repeatedly microwaving melamine-formaldehyde tableware could increase migration levels of methylol melamine derivatives. The researchers found that 25 heating cycles in a microwave, using acetic acid to simulate food, led to chemical releases exceeding EU migration limits. Further investigation revealed a lack of methylene linkages, indicating that the plastic may not have been cured fully.