Hazard Assessment and Contaminated Sites - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 555

Table 12.4 Toxic
equivalency factors (TEFs)
for human and mammalian
Risk Assessment

Congener (Dioxins) WHO TEF

2,3,7,8 - TetraCDD 1

1,2,3,7,8 - PentaCDD 1

1,2,3,4,7,8 - HexaCDD 0.1

1,2,3,6,7,8 - HexaCDD 0.1

1,2,3,7,8,9 - HexaCDD 0.1

1,2,3,4,6,7,8 HeptaCDD 0.01

OctaCDD 0.0003

CDD Chlorinated dibenzodioxin

Where contaminants share structural similarities such as Dioxins, PCBs and
Polycyclic Aromatic Hydrocarbons the use of Toxic Equivalency Factors has been
proposed. Different contaminants are given toxicity “scores” that are fractions of
the toxicity of another in the chemical group for which there is adequate toxicity
data. Given a mixture of the contaminants, a cumulative toxicity score can be deter-
mined. The IPCS has published TEFs for several dioxins and these are shown in
Table 12.4 .
World Health Organization (WHO) The WHO re-evaluation of human and mam-
malian toxic equivalency factors (TEFs) of dioxins and dioxin-like compounds (van
den Berg et al. 2006 ).
Biological methods such as bioassays are being appraised for their application
to the assessment of the toxicity of mixtures. Rodents or other mammals may be
administered extracts so that a toxicity value such as an LD 50 can be determined.
These methods are expensive and time consuming which usually precludes their use
in Risk Assessment. Similar techniques using aquatic species such as Daphnia are
less expensive and time consuming, but are disadvantaged by the greater toxicoki-
netic and toxicodynamic differences between the species used and humans (Pollak
1996 ). There are in vitro tests such as the Microtox test and the Submitochondrial
Particle Test, but these require validation for use in Risk Assessment.
Useful information for exposures to mixtures of hazards may be available from
epidemiological studies of similar or closely similar mixtures.

12.5.10 Checklist for Toxicological Appraisals

The following checklist is adapted from US EPA ( 1995 ) and can be used when
appraising toxicological information.

12.5.10.1 Hazard Identification

1. What is the key toxicological study (or studies) that provides the basis for health
concerns?