A farm is identified to contain Arsenic $($As$)$ contaminated soil. There are $4$ buildings in the farm. Two of the buildings are residential, third is a horse stable with paved floor and fourth building is an indoor horse$-$riding arena. All the three buildings, except the arena, and the front parking covers $1/3$ of hectare and is assumed to be free of As contamination. The other $2/3$ hectare is grazing area behind the buildings is however contaminated with As$.$ The floor of indoor horse arena is filled with the soil from grazing area, thus also contaminated with As$.$ There are two adult people living and working in the farm. One of them is horse riding instructor and spends $8$ hrs daily, $5$ days a week, in the indoor horse arena. The other person works in the grazing area for $8$ hrs daily and they always stick to their roles. The riding instructor always wears high boots $($riders$$ boots$)$ and helmet while in the arena leaving only his hands and arms exposed. Ground water well is the primary source of water to animals and people of the farm. All the water in the farm is assumed to be uncontaminated. Assume any data not given.

Concentration of Arsenic in soil of grazing area and indoor arena $300$ mg$/$kg dw soil

Soil loading factors $1*10-8$ kg$/$cm$2/$event Consider this same loading factor for hands, legs, arms, feet and head.

Human gastrointestinal absorption factor $1($unitless$)$

Human inhalation absorption factor $1($unitless$)$

Oral Slope factor for Arsenic $1\mathrm{.}5$ per mg$/$kg$-$day

Assume same for dermal exposure.

a$)$ What is the risk from cancer due to As soil ingestion for the riding instructor?

b$)$ What is the risk from cancer due to As dermal contact for the riding instructor?