Freezing of samples is not directly referenced as an acceptable method of sample preservation in Canadian environmental regulations.
However, certain EPA reference methods do list sample freezing as being an acceptable approach, for certain organic parameters.
One of the concerns with freezing environmental samples is loss of target parameters that are volatile, during the thawing process. Therefore, providing an accurate account of how the data may be impacted due to accidental freezing is very difficult.
The data associated with such samples would certainly be qualified (commentary to indicate that samples were received frozen and were slowly thawed at temperatures just above 0C). No assessment of the impact to the data would be given since the starting point for target parameter(s) concentration is unknown. As well, it may very well be that there is no significant impact to the data reported.