I doubt that you could determine, by looking at a particular individual, the
likely cause of an anatomical malformation .  In general, I think that
aberrations caused by pollution would tend to be more commonplace in a given
locality than those caused by naturally occurring random genetic mutation.
A random mutation may affect only one individual in a population of
millions, whereas large numbers of individuals in a given locality would be
exposed to any major source of pollution.  However, not all individuals
receiving similar exposure would be similarly affected. Genetic
abnormalities are not completely separable from those caused by pollution,
since one of the ways pollution can case abnormalities is by inducing
chromosomal damage.  In other words, some genetic malformations have an
underlying chemical cause.  Also, some individuals in a population may be
genetically predisposed to damage from a specific chemical cause.  That is,
some individuals, by virtue of their normal genetic makeup, may be highly
susceptible to a particular pollutant, while others may be relatively
resistant.  This is part of the reason why one person may smoke three packs
of cigarettes a day for 50 years and not develop lung cancer, while another
person may develop the disease from 10 years of exposure to second hand
smoke.  So, genetic and environmental causes are rather intricately
intertwined, and it can be pretty difficult to separate one from the other.
Paul M.