It is shown for the first time that the volatile highly chlorinated C2 hydrocarbons (VCHCs) trichloroethene (TRI; C2HCl3), tetrachloroethene (PER; C2Cl4) and methyl chloroform (MC; C2H3Cl3), but also C1 hydrocarbons tetrachloromethane and chloroform can be naturally formed in the sediment of salt lakes (ssl). Archaic halobacteria appear to play a key role in the microbial formation involved. TRI, PER and MC can be transformed into trichloroacetic acid (TCA) in the atmosphere. TRI and PER can also be metabolised into TCA following uptake by plants. Already considerably phytotoxic by itself, TCA's phytotoxicity is exacerbated if the vegetation concerned is simultaneously exposed to drought-stress. TRI and PER, emitted by these newly identified natural sources, can accelerate desertification in semi-arid and arid climate zones in consequence of the destabilisation of vegetation by its phytotoxic metabolite TCA.