In experiments it has sometimes been observed that the DDT decomposes to a certain extent under microbial influence, these results are, however, still contradictory
(Fries 1972). The breaking down of dieldrin, lindan and endrin is more effective
under certain conditions, with the participation of bacteria and soil fungi. In the
ocean, too, microorganisms to a large extent break down DDT into DDD [also known
as TDE; 1 ,2-dichlor-2,2-bis (p-chlorophenyl) ethane ]. In animals and other organisms,
as well as under the influence of sunlight, DDT is broken down to DDE [1 ,1-dichloro2,2-bis(p-chlorophenyl)ethylene]. DDD and DDE, however, differ only slightly from
DDT in their toxicity and are largely persistent, except to further decomposition into
similar chemical compounds. After a careful analysis one also discovers polar components that signalize a further decomposition of DDT compounds (Ernst and Goerke
1974). Such components were found in experiments with sole (Solea solea) but there
are indications that these components are not produced by the sole themselves but
rather by the bacterial flora in the sole's gut. In the feces of guillemots (Uria aalge)
and grey seals (Halichoerus grypus) of the Baltic Sea phenolic metabolic products of
DDT and PCB's were found that indicate a special metabolism of these warm-blooded
animals. The PCB compound here also differs from that of their prey, the herring
(Clupea harengus) (Jansson et al. 1975). If one feeds polychaetes (Nereis vuens) with
PCB's, most of them are excreted unaltered with the feces, but polar break-down
products can also be found in the feces, among others trichlorobiphenylol (Ernst
et al. 1977; Ernst 1980).
Under anaerobic conditions mixed cultures of marine bacteria found near the coast
metabolize PCB's into an acid lactone metabolite (Carey and Harvey 1978). In general,
bacteria that decompose PCB's can be found in estuaries, especially near industrial
plants (Sayler et al. 1978).
It is also known that under anaerobic conditions, such as can be found in sewage
sludge in sewage treatment plants as well as in the deeper layers of marine sediments,
bis-(p-chlorophenyl)-acetonil develops from DDT (Jensen et al. 1972). These are,
however, conversions that only affect a minor part of the DDT, and the question is
what Significance these conversions observed in the laboratory have in natural surroundings (Addison 1976). For the moment the allegation that a number of chlorinated hydrocarbons, among others DDT and PCB's, are to a large extent persistent,
remains valid: they are broken down to harmless components neither through hydrolysis in water, nor through microbes nor in the metabolism of other organisms, and
the ultraviolet rays of the atmosphere have only a limited effect.
Various speculations have been made about the amount of DDT that may have
entered the world oceans over the last decades. Supposing 50% of the DDT used
enters the atmosphere (Butler et al. 1972), then 700,000 t of the 2.8 million t of
DDT produced until 1974 still ought to be in the oceans. With an ocean area surface
of 3,6 X 10 14 m 2 this amounts to approximately 2000 f.l.g/m 2 or with a median
water depth of 3700 m this means 0.5 f.l.g DDT/m 3 water, resulting in a concentration of 0.5 ng/I. In 1970 approximately 100,000 t of DDT were used; if 25% of this,
or 25,000 t, entered the ocean it would imply a fall-out of 70 f.l.g/m 2 . In the biologically important, 100-m-deep surface layer of the ocean, this would imply an input of
0.7 ng of DDT per liter of seawater. These figures correspond with those found by
measurements of DDT contents in rainwater. The annual precipitation into the ocean
176
(Fries 1972). The breaking down of dieldrin, lindan and endrin is more effective
under certain conditions, with the participation of bacteria and soil fungi. In the
ocean, too, microorganisms to a large extent break down DDT into DDD [also known
as TDE; 1 ,2-dichlor-2,2-bis (p-chlorophenyl) ethane ]. In animals and other organisms,
as well as under the influence of sunlight, DDT is broken down to DDE [1 ,1-dichloro2,2-bis(p-chlorophenyl)ethylene]. DDD and DDE, however, differ only slightly from
DDT in their toxicity and are largely persistent, except to further decomposition into
similar chemical compounds. After a careful analysis one also discovers polar components that signalize a further decomposition of DDT compounds (Ernst and Goerke
1974). Such components were found in experiments with sole (Solea solea) but there
are indications that these components are not produced by the sole themselves but
rather by the bacterial flora in the sole's gut. In the feces of guillemots (Uria aalge)
and grey seals (Halichoerus grypus) of the Baltic Sea phenolic metabolic products of
DDT and PCB's were found that indicate a special metabolism of these warm-blooded
animals. The PCB compound here also differs from that of their prey, the herring
(Clupea harengus) (Jansson et al. 1975). If one feeds polychaetes (Nereis vuens) with
PCB's, most of them are excreted unaltered with the feces, but polar break-down
products can also be found in the feces, among others trichlorobiphenylol (Ernst
et al. 1977; Ernst 1980).
Under anaerobic conditions mixed cultures of marine bacteria found near the coast
metabolize PCB's into an acid lactone metabolite (Carey and Harvey 1978). In general,
bacteria that decompose PCB's can be found in estuaries, especially near industrial
plants (Sayler et al. 1978).
It is also known that under anaerobic conditions, such as can be found in sewage
sludge in sewage treatment plants as well as in the deeper layers of marine sediments,
bis-(p-chlorophenyl)-acetonil develops from DDT (Jensen et al. 1972). These are,
however, conversions that only affect a minor part of the DDT, and the question is
what Significance these conversions observed in the laboratory have in natural surroundings (Addison 1976). For the moment the allegation that a number of chlorinated hydrocarbons, among others DDT and PCB's, are to a large extent persistent,
remains valid: they are broken down to harmless components neither through hydrolysis in water, nor through microbes nor in the metabolism of other organisms, and
the ultraviolet rays of the atmosphere have only a limited effect.
Various speculations have been made about the amount of DDT that may have
entered the world oceans over the last decades. Supposing 50% of the DDT used
enters the atmosphere (Butler et al. 1972), then 700,000 t of the 2.8 million t of
DDT produced until 1974 still ought to be in the oceans. With an ocean area surface
of 3,6 X 10 14 m 2 this amounts to approximately 2000 f.l.g/m 2 or with a median
water depth of 3700 m this means 0.5 f.l.g DDT/m 3 water, resulting in a concentration of 0.5 ng/I. In 1970 approximately 100,000 t of DDT were used; if 25% of this,
or 25,000 t, entered the ocean it would imply a fall-out of 70 f.l.g/m 2 . In the biologically important, 100-m-deep surface layer of the ocean, this would imply an input of
0.7 ng of DDT per liter of seawater. These figures correspond with those found by
measurements of DDT contents in rainwater. The annual precipitation into the ocean
176