Arsenic or Cyanide ?

Seeds of fruits like apples, cherries, apricots, etc., do not contain any arsenic. Arsenic is a heavy metal that is too difficult for a plant's metabolism to process, any amount of it would likely kill of the plant. The only time arsenic is likely to be present is if it had been used as a form of fungicide/herbicide spray during the culivation of the fruit (very unlikely these days - I think its mostly outlawed), and hadn't been properly washed off.

Plants do however have the ability to work with vast amounts of carbon and nitrogen, this results in most hard seeds containing cyanide (the cyanide radical is CN-). Not really enough to injure anyone, infact commercially made Kirsch (cherry brandy) uses ground up seeds to give a nut like flavor (cyanide tastes kind of like an intense bitter almond flavor). In some recipes grinding up the seeds of delicate tasting fruits should be avoided but with something more robust (like apple), it should be of no concern.

Wal elaborates ...
    The kernels of prunus species (plums, cherries, apricots, apples) contain HCN - hydrocyanic acid, formerly known as prussic acid. 0.05g is a lethal dose for an adult. It has been recorded that a person died from eating a whole cup of apple pips as a treat on his birthday! Normally, when macerating these fruits in alcohol, the stones should be removed, although small amounts are used for flavoring purposes (e.g. Maraschino).

    Fruit mashes (i.e. with stones included) should not be a problem for the distiller, as HCN is susceptible to hydrolysis at high temperatures.
Zoran writes that it is possible to remove any cyanide present, using copper sulphate:
    in Serbia the national drink is a plum brandy called slivovitz. If someone tries to speed up fermentation by crushing plums with some mechanical devices, natural glycosides come in contact with the enzymes present. After hydrolysis, a bitter taste and smell is a consequence of the cyanide present. After distillation farmers do not throw away such brandy. Simply they put 20 g of CuSO4.5H2O on each 10 L of 80 proof (40%) brandy. Chemically Cu(CN)2 is very hard do dissolve, even at high temperature. After distillation they got good drink. Big companies remove cyanide in the same way.

Esters and especially organic acids arise from misfermentations of leafs/twigs or rotten parts of fruit, so try to avoid having them in the brew.
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