Both are type of chromosomal damage
1. clastogenic is chromosome breakage
2. Aneugenic, that causes a daughter cell to have an abnormal number of chromosomes.
Here i am telling you, however u cannot really say which is more serious. Anything that turns out to be fatal is serious... And both have the potential to turn out to be fatal. Both cause the disaster condition in organisms but comparatively aneugenic is more dangerous because it creates birth defects and passes into ongoing progeny of the organisms.
It depends on the type of cells. Both, clastogens and aneugens may induce cancer in somatic cells, AND congentital malformations in the germ cells. E.g. Trichlorfon is an environmental aneugenic compound. When it acts as an aneugen in germ cells or in embryonic cells it will lead to multiple congenital malformations. At the same time it is still not known whether it is clastogenic at certain concentration in somatic cells.
aneugenic may lead to loss of chromosome and can be dangerous more than clastogeny as the latter only destroys segments of chromosome.