Do sins or touching impurities invalidate Wudu, and what is the evidence for that?

Sins such as backbiting and lying do not nullify ablution. To claim otherwise would require evidence, and there is no indication that sin affects ablution. What has been reported from some of the Salaf regarding the command to perform ablution after certain sins is interpreted as an intention to emphasize severity or as a recommendation to perform ablution, because ablution expiates sins.

As for touching impurities, it does not nullify ablution. So, if one touches blood or urine, ablution is not invalidated, but what was touched should be washed.