Lake environments - Environmental Sedimentology - page 132

Table 4.11 Some well-known chlorinated organics.

Contaminant Details

TOCl Total organically bound chlorine

AOX Adsorbed organically bound halogen

EOCl Extractable organically bound chlorine

EPOCl Extractable (acid-)persistent organically bound chlorine

Dioxins Polychlorinated dibenzo dioxins (PCDD); and furans; there are many dioxins and furans, of which,

'the dirty dozen', are considered of special interest in ecotoxicology

PCB Polychlorinated biphenyls; lipophilic substances used, e.g. in oils; certain forms, such as planar PCBs

are considered to be responsible for the sterility of Baltic seals

DDT Dichlorodiphenyltrichloroethane; this group includes, e.g. lindane, aldrine, dieldrine and

dichlorodiphenyldichloroethylene (DDE), all well-known from R. Carson's topic Silent Spring

HCB Hexachlorobenzene

HCH Hexachlorocyclohexane

potential (Eh) often increase metal toxicity. The
solubility of most heavy metals increases at
decreasing pH and metals that previously have
been bound in rather harmless particulate forms
in the sediments may be recirculated to the
lake water and express their toxic properties if
sediment pH or Eh changes. The roles of heavy
metals are, as stressed, complicated by the fact
that some of them are essential in small amounts
for the organisms.
Table 4.11 gives one example of how to struc-
ture the very complex group of organic toxins.
For example, AOX stands for adsorbed organic-
ally bound halogen, TOCl for total chlorinated
organic material, EOCl for extractable organ-
ically bound chlorine, EPOCl for extractable
persistent organically bound chlorine, etc. The
focus of many studies has been on emissions
of chlorinated substances from paper and pulp
mills (see Södergren 1992). In sediments, only
about 2% of a sum-parameter such as TOCl
consists of EOCl, and only a small fraction (

(1992) gives a thorough evaluation of biological
effects of bleached pulp mill effluents in the
Baltic.
In summary, the major threats from chemical
pollutants today concern nutrients (phosphorus
and nitrogen) causing different types of
eutrophication effects (Ambio 1990; Wallin
et al. 1992), toxic substances such as metals
(Cd, Pb, Cu; Förstner & Müller 1974), chlori-
nated organics (e.g. PCBs, DDT, dioxins;
Södergren et al. 1988) and acidification of land
and water, its ecological damage and economic
consequences (Ambio 1976; Likens et al. 1979;
Merilehto et al. 1988). Case Study 4.1 gives an
example of EOCl contamination.

4.3.5 Climatic change

Many lakes are highly sensitive to changes in
temperature and precipitation (both magnitudes
and frequencies; see Intergovernmental Panel on
Climate Change (IPCC) website), because this may
influence fundamental processes related to lake
ecosystem structure and functioning (e.g. rates
of evaporation, lake water level and production
and biomass of key functional groups or species).
Under extreme climatological conditions, very
shallow lakes may even disappear. Responses
to climate change will also vary between lakes
at different latitudes, altitudes and depending
on physical geographical conditions. Lakes, and
especially lake sediments, are good sources of
information about past climatic/environmental

1%)
of EOCl consists of chemically identified sub-
stances, specific parameters, such as dioxins,
polychlorinated biphenyls (PCBs) or dichloro-
diphenyltrichloroethane (DDT). The toxicity of
organic pollutants, such as EOCl, DDT and
PCB, may be manifested in many different ways,
for example increased fin erosion in perch,
increased frequencies of skin ulcers in herring
and increased skeleton deformations, such as
deformed jaws in pike or spinal column bending
in fourhorn sculpin (Bengtsson 1991). Södergren

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