Large quantities of industrial by-products like steel slag, fly ash and bottom ashare produced as residues. A fraction of these by-products are being reused in structural
fills and roads while the rest is being disposed in landfills. If the use of these by-products
in roads as base layers is encouraged then we can save on the environmental
contamination that the extraction of natural aggregates causes. Large areas of land are
allocated for landfill sites. If the by-products are reused in roads then we can save on the
land sites and also save on the costs of extraction (mining, crushing etc) of the natural
aggregates.
This research calculates the possible human health risks to construction workers
working with the by-products in road construction. This thesis also calculates the risk to
groundwater due to the placing of these by-products in road base layers. The risk model
was created to assess the risk to construction workers and groundwater also incorporates
results from a fate and transport model, HYDRUS for assessing the risk to groundwater
In risk assessment for construction workers, average daily dose (intake) of each
constituent metal of the industrial waste material to a construction worker was calculated.
The calculated average daily dose was compared with reference dose and slope factors of
that metal to find the carcinogenic and non-carcinogenic risk pertaining to the ingestion,
dermal contact and inhalation of by-products. The industrial by-products placed in the
base layers of the roads can seep through the soil profile and enter the ground water table.
The concentrations that ultimately reach the ground water were calculated using
HYDRUS. The results from HYDRUS were plugged back in the excel model to assess
the risk to ground water. The concentrations of the metals in ground water were
multiplied with their slope factors to obtain carcinogenic risk, and the same
concentrations in ground water were divided over the reference dose to obtain the noncarcinogenic
risk The risk value should be less than 1 in a million to term “no risk” due to
carcinogenic effects from that metal to humans and the value for hazard quotient for noncarcinogenic
risk should be less than 1.
The results from the risk model suggested no carcinogenic risk due to inhalation to
construction workers from any of the slag types in road construction. However, some
constituent metals in the steel slag appeared to pose a carcinogenic risk due to particulate
ingestion. These were chromium and beryllium in all the slag types and cadmium and
nickel causing risk only in basic oxygen slag and electric arc furnace slag. When the noncarcinogenic
risk was assessed of various types of steel slag for construction workers,
there were some hazard quotiont values higher than 1, the target risk value. The high risk
values in the results suggest that a probabilistic risk approach should be adopted rather
than a conservative and deterministic present approach. Also limitations of data on bioaccessibility,
reference dose and slope factors contributed to high risk values in this
research.