The effects of organolead compounds on a freshwater and a marine alga

There are conflicting reports concerning the toxicity of tetraalkyllead (TAL) compounds to algae. A number of groups have found the TAL's to be comparable in toxicity with the trialkyllead compounds (R₃Pb⁺), whereas in a recent report it is suggested that the TAL's themselves are completely non-toxic and any apparent toxicity is due to R₃Pb⁺ breakdown products. With the object of identifying the toxic agent, the effect of Et₄Pb (TEL) on two algal species was re-examined. Analyses were carried out during the course of the incubations to establish the nature and concentrations of organoleads present in both media and algae, and hence evaluate their relative contributions to total toxicity. Algae were also cultured in the presence of Me₄Pb (TML), Me₃PbCl, Et₃PbCl, Bu₃PbCl and Et₂PbCl₂ to assess relationships between alkyl chain length and degree of substitution around the lead on algal activity. Additions of selenide and sulphide were made to the Et₃Pb⁺ and Et₂Pb²⁺ systems to see if these environmentally abundant species reduced or enhanced organolead toxicity. Problems were encountered in the analysis of the heterogeneous TEL containing media. Regardless of the analytical problems, the results confirm the previous findings that TAL's are non-toxic to algae and it is the R₃Pb⁺ breakdown products which are responsible for the apparent toxicity of the TAL's. The trialkylleads were the most toxic of the several alkyllead species studied, and within the trialkyl series toxicity increased with alkyl chain length. Neither selenide or sulphide had any significant ameliorative effect on alkyllead toxicity. It was found that the ionic organoleads were complexed on the TAL's and this complexing led to a number of unexpected results.