Natural Formation of Chlorobenzoic Acids

V. W. Niedan Institut für Umwelt-Geochemie, Universität Heidelberg, INF 236, 69020 Heidelberg, Germany

H. F. Schöler Institut für Umwelt-Geochemie, Universität Heidelberg, INF 236, 69020 Heidelberg, Germany

Naturally produced organohalogens are of enormous interest due to their almost ubiquitous occurence in the biosphere, their toxic and cancerogenic activity, and their environmental relevance. If a naturally produced organohalogen can stem also
from anthropogenic sources, it is difficult to discover them and make a distinction whether they are formed naturally or

Chlorobenzoic acids (CBAs) are well known as metabolites during PCB degradation (Flanagan and May, 1993). We found CBAs in two unpolluted marshy ponds (called Rotwasser and Hohlohsee, situated in natural reserves) and in spring water from the Vosges. The main CBA was always the 2,4-isomer (up to 0,4 µg/l). 2,5-CBA was detected in 2-10 times smaller content. There are several indications that the detected CBAs stem from a natural production and not from a PCB-degradation:

- the main metabolite of PCB degradation is the 2-CBA (and not the 2,4-isomer).

- the concentrations of the 2,4-CBA correlate with pH, temperature and DOC of the samples. These circumstances influence the activity of microorganisms which produce the chlorinating responsible enzyme Chloroperoxidase (CPO). The activity of CPO is also dependant on these factors.

- the concentrations of the 2,4-isomer also correlate with the trichloroacetic acid concentrations which is known as a
naturally produced organohalogen (Haiber et al., 1995; Hoekstra et al., 1995).

- we could detect CBA in a reaction of benzoic acid with CPO.

There is a strong indication that if there were only 2,4- and 2,5- CBA as dichlorobenzoic acids (with a ratio about 2-10:1, and smaller amounts of 2- and 4-CBA detectable), that these CBAs do not originate from PCB degradation but from natural production.


Flanagan, W.P. & May, R.J. Environ.Sci.Technol. 27, 2207-2212 (1993).

Haiber, G., Jacob, G., Niedan, V.W., Nkusi, G. & Schöler, H.F., submitted to Chemosphere (1995).

Hoekstra, E.J., Lassen, P., van Leuwen, J.G.E., de Leer, E.W.B. & Carlsen, L., In Naturally Produced Organohalogens (Grimvall, A. & de Leer, E.W.B., ed.) 149-161 (Kluwer Academic Publishers, Dordrecht, Boston, London, 1995).