DEFINITIONS

According to the new Technical Guidance Document bioconcentration is defined as the net result of the uptake, distribution, and elimination of a substance in an organism due to water-borne exposure, while bioaccumulation includes all routes, i.e air, water, soil, land and food. One way to assess a chemical risk for bioaccumalation inaquatic species is to measure the bioconcentration factor (BCF). The Bioconcentration factor is expressed in l/kg b.w and it is defined as the aquatic organism/water concentration ratio once reached the steady-state situation.

USEFUL DATA

Early experimental studies on bioconcentration of LAS (reviewed by Tolls et al., 1994) were not appropriate because of the analytical methods based on radio-analysis, which consistently overestimated the parent concentration present in the aquatic organism and consequently the true bioconcentration. An in depth research project on bioconcentration of surfactants was recently completed (Tolls, 1998).

LAS was studied employing a flow-through test system, in line with the OECD guidelines, using Pimephales promelas as test fish. Single homologues and isomers representatives of commercial LAS were synthesized and then tested, determining their uptake and their elimination rates in fish. Specific HPLC analysis in the water phase and in the fish body showed that LAS reaches a steady state concentration in the fish body in about 3 days.

Biotransformation contributes to more than 40% of the elimination as shown for the C_12-2-LAS homologue (Tolls et al., 2000). BCF data for the tested LAS standards ranged between 2 to 990 l/kg, allowing calculating the potential BCF of any LAS mixture (Tolls et al., 1997). Commercial LAS, C_11.6 alkyl chain length, has BCF = 66 l/kg, whereas the mixture usually present in water, C_10.8 alkyl chain length (see 4.1.3), has BCF = 16 l/kg (Tolls, 1998, pp175).

In view of the realistic data on the bioconcentration of LAS it is concluded that this surfactant doesn't represent a concern both to human health and to aquatic safety.

Key references

Tolls J, P Kloepper-Sams, DTHM Sijm, Surfactant bioconcentration. A critical review, Chemosphere 29: 693-717, 1994

Tolls J, M Haller, I DeGraaf, MATC Thijssen, DTHM Sijm, Bioconcentration of LAS. Experimental determination and extrapolation to environmental mixtures, Environ. Sci. Technol. 31: 3426-3431, 1997

Tolls J, Bioconcentration of surfactants, Thesis, ISBN No.: 90-393-1676-1, Utrecht University, 1998

Tolls J, MP Lehmann, DTHM Sijm, Quantification of in vivo biotransformation of the anionic C_12-2-LAS in tathead minnows, Environ. Tox. Chem. 19: 2394-2400, 2000