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  • In this booklet we have used the following format for expressing units followed by their characterization and matrix information in parenthesis: 10 ng/kg (WHO-TEq in fat)
  • Σ (sigma), sum. Ordered alphabetically at the main entry disregarding the prefix (e.g. Σ7PCB, see PCB).
  • b.w., body weight.
  • deka-, ten. E.g., dekachloro- ten chlorine atoms in a molecule.
  • di-, two. E.g., dichloro- two chlorine atoms in a molecule.
  • d.w., dry weight.
  • hepta-, seven. E.g., heptachloro- seven chlorine atoms in a molecule.
  • hexa-, six. E.g., hexachloro- six chlorine atoms in a molecule.
  • microgram (µg), 0.000,001 g. See units.
  • mono-, one. E.g., monochloro- one chlorine atom in a molecule.
  • nanogram (ng), 0.000,000,001 g. See units.
  • ng, nanogram. See units.
  • nona-, nine. E.g., nonachloro- nine chlorine atoms in a molecule.
  • octa-, eight. E.g., octachloro- eight chlorine atoms in a molecule.
  • ΣPCB, the sum (total weight) of all PCB congeners.
  • Σ7PCB, the sum (total weight) of the seven marker PCBs (see this).
  • ΣPCDD/F, the sum (total weight) of the 17 PCDDs and PCDFs with a TEF value >0.
  • penta-, five. E.g., pentachloro- five chlorine atoms in a molecule.
  • picogram (pg), 0.000,000,000,001 g. See units.
  • ppb, parts per billion (American). A non-standard concentration unit equal to ng/g or µg/kg or 10-9 g/g.
  • ppt, parts per trillion (American). A non-standard concentration unit equal to pg/g or ng/kg or 10-12 g/g.
  • tetra-, four. E.g., tetrachloro- four chlorine atoms in a molecule.
  • tri-, three. E.g., trichloro- three chlorine atoms in a molecule.
  • Units. Concentrations and amounts of dioxins and PCBs are very small, and therefore units to measure them do not belong to everyday vocabulary (Table 5.). One picogram per gram results, if 10 g (a spoonful of sugar) is dissolved in a lake 10 m deep and one square kilometre large. These small concentrations we are dealing with explain why rather small amounts of chemicals can contaminate large amounts of feed, for instance. PCDD/F concentrations are often expressed as TEq (see this). PCB is usually expressed as sum of all PCBs (ΣPCBs) or as sum of marker PCBs analysed (e.g. Σ7PCBs, sum of seven marker PCBs [see this]). Concentrations of PCBs or PCDD/Fs can be expressed per wet weight (w.w.) (e.g. in fish), per dry weight (d.w.) (e.g. in soil), per normalised cubic meter (Nm3) (e.g. in exhaust gases), or per fat. Many organisms contain about 10 % fat, then the difference between concentrations per fat and per wet weight is about tenfold. However, especially fish may be very different in their fat content, and usually PCBs and PCDD/Fs in fish are given per wet weight. Human PCBs and PCDD/Fs are mostly expressed per gram fat, because the concentrations are comparable regardless of if it was measured in serum, adipose tissue or milk. Human body contains about 15 % (10 -12 kg) fat, but the variation is large, especially upward. See also Common sources of errors and practical difficulties in General introduction.

Table 5. Weight units.

1 kg (kilogram) 1000 g  103 g
1 g (gram) 1 g 100g
1 mg (milligram) 0.001 g  10-3 g
1 µg (microgram)  0.000,001 g 10-6 g
1 ng (nanogram) 0.000,000,001 g 10-9 g
1 pg (picogram) 0.000,000,000,001 g 10-12 g
1 fg (femtogram) 0.000,000,000,000,001 g 10-15 g