Why is Thallium More Toxic than Other Boron Group Elements?

[Calpalned]

I am confused as to why thallium is toxic, while the other members of group 13 are safe?

(Quotes are from Wikipedia)
Boron - "Elemental boron [is] non-toxic to humans and animals"
Aluminum - "... [has] extremely low acute toxicity..."
Gallium - "...metallic gallium is not considered toxic..."
Indium - "...is not a toxic hazard."
Thallium - "Thallium and its compounds are extremely toxic"

Why is this the case? It seems that I can touch boron, aluminum, gallium and indium with my bare hands, but not thallium. I don't understand this.

Thanks.

 

[Borek]

While the elements in a group bear some similarities, they are also different. Nothing surprising about it.

 

[Suraj M]

Tl⁺ in aqueous solution behaves like Potassium, it is absorbed into the body by potassium pathways, and then it accepts sulphur complexes (ligands). This is harmful to cellular processes whereas In³⁺ doesn't.
Bottom line,As borek said there are just similarities between members of the same group. In that way you may ask most elements prefer a Oxi. state of 3+ but Thallium(to an extent In) sow Oxi. state of 1+. It happens due to variations with increase in atomic number. :)