It's natural concentration is 0.015 m g/l in sea water. The origin of pollution due
to emissions coming from the human activities is varied. Primarily, it originates in the
foundries of the metallurgy and the incinerators of refuse. Then come the paintings
carried out with compounds from sulphates and of basic lead, certain lead alloy
insecticides and sleeving also pollute the medium out of lead.
The total lead discharge in water is 3.8 million kg.
Consequences
of a pollution by lead, of its impact on the marine flora were studied in laboratory on
unicellular algae in cultures constituting a simple tool for the researchers. This study,
under taken in particular on Bacillariophycées (diatoms), seems to show that in some
cases lead tends to support the growth of the algae with relatively weak concentration;
but with more raised concentration, the toxic effects occur (Study of Jenning in 1979;
Stromgren, 1980). Rachlin and al.(en 1983) determine the effective concentration reducing
the phyto-planktonique growth of 50% for various species. It is of 6.1 mg/1 for the
species Nitzschia closterium (Bacilariophycées).
The growth of the alga Asparagopsis armata is slowed down starting from a
concentration of 3.7 mg/I (Sergot and Al 1983)
In 1980, Stromgen reports that lead has negative effects on the growth of
these three algae: Wrackspiralis, Wrack serratus and Ascophylum nodosum ,
starting from concentration higher than 2mg/1. It connects this toxicity to the fact that
with these concentrations, lead precipitates and absorbs it self on the algae. On the
other hand, with weaker concentration (45-810 Mg /
L), the growth of the alga Pelvetia
caniculata is favoured.
