The term bioindicator is used for organisms or organism associations which respond to pollutant load with changes in vital functions, or which accumulate pollutants (Arndt et al. 1987). Information about specific biological effects supplements data on air pollutions generated by technical analysis methods. The most important reasons for using bioindicators are:
- the direct determination of biological effects,
- the determination of synergetic and antagonistic effects of multiple pollutants on an organism,
- the early recognition of pollutant damage to plants as well as toxic dangers to humans and
- relatively low cost compared to technical measuring methods.
The great potential of bioindicators for environmental monitoring is often confronted with difficult questions of methodology resulting from the use of “living measuring instruments”. The effects of environmental load cannot always be clearly differentiated from natural stress factors. Lack of practical experience with certain bioindicators sometimes makes clear interpretation of findings more difficult, especially if no comparable pollutant measurements are available.
Intensive research over the last decades has resulted in the availability of numerous bioindicators which satisfy the requirements of convenience, standardization, cost, and evaluative capability (cf. Arndt 1987, Zimmermann u. Umlauff-Zimmermann 1994).
Bioindicators are commonly grouped into accumulation indicators and response indicators. Accumulation indicators store pollutants without any evident changes in their metabolisms. Response indicators react with cell changes or visible symptoms of damage when taking up even small amounts of harmful substances.
Biomonitoring is divided into passive and active. Passive biomonitoring is the use of organisms, organism associations, and parts of organisms which are a natural component of the ecosystem and appear there spontaneously. Active biomonitoring includes all methods which insert organisms under controlled conditions into the site to be monitored.
Cadastre of Ecological Pollution Effects
The Berlin Department of Urban Development, Environmental Protection, and Technology has conducted comprehensive studies for the determination of air pollution effects since 1991. These studies emphasized the complex of pollutants typical for metropolitan areas (SenStadtUm 1993a). All bioindicator methods employed have advantages and disadvantages. This means in practice that not only individual bioindicators, but a whole series of bioindicators was employed, according to the particular goal. This series is as finely adjusted to each other as possible. The systematic use of bioindicators was used for the Cadastre of Ecological Pollution Effects, conducted for the Ecological Monitoring Berlin and Hinterland. The findings are important supplements to and extensions of air quality monitoring data, especially for the year-long random sample measurement program of the Berlin Air Quality Monitoring System – BLUME.
A great amount of data and knowledge has been generated by the Cadastre of Ecological Pollution Effects. The size of this data requires presentation in the Environmental Atlas to be limited to findings which have been sufficiently secured. These findings allow a differentiation of pollutant load ranges and could serve as a particularly significant basis for planning.
The Environmental Atlas took active and passive bioindicator methods, as well as accumulation and reaction indicators (cf. Fig. 1) almost equally into consideration. The selected results allow an overview of general air pollution in Berlin, manifested by effects upon naturally occuring lichen and exposed lichen transplants, as well as an overview of regional pollutant patterns, indexed by accumulation in pine needles, rye grass, and green kale.
Findings of the Cadastre of Ecological Pollution Effects not presented here (cf. Fig. 1) can be found in various studies and publications (cf. Literature).
The evaluation of study findings can, in some cases, be supplemented by earlier research. This enables a chronological comparison of general pollutant effects and certain pollutant materials (cf. Cornelius et al. 1984). These kinds of reference data are valuable yardsticks for evaluation of the current pollutant situation in Berlin, for changes in air quality over recent decades can thus be documented.
The selection of analyzed pollutants took into consideration human toxicity, phytotoxicity, and ecosystem aspects. The information can thus be used for an overview of environmental loads in the Berlin area. The Cadastre of Ecological Pollution Effects focused mainly on the pollutants described below.
Until the end of the 80’s, Berlin air had relatively high SO2 and dust pollutions, especially during low-exchange winter weather periods. This was mainly due to the large amounts of sulfur-rich lignite brown coal used for heating in older residential areas (cf. Map 03.01, SenStadtUm 1994).
SO2 in the air enters plants as a gas or in water solution and can cause damage. Chemical reactions of SO2 create acids. Precipitation can transport these acids into the soil and trigger indirect damages, such as lack of nutrients and acid stress. Value limits for direct damaging effects on plants are clearly lower than for animals and humans. High sulfur dioxide concentrations lead to air pollution damages on coniferous trees, including non-specific chloroses, necroses, growth inhibition, and impairment of reproduction.
Lead is a heavy metal and has special environmental relevance because it is toxic. Leaded gasoline is still the main source. Most lead particles remain on the surface of leaves. Only a small amount becomes physiologically active and damages plants. This process can lead to accumulation in the food chain. Toxic effects for grazing animals or humans cannot be ruled out.
Fluorine is released from various industrial processes, waste burning, and by fossil fuel energy production. Hydrogen fluoride damages in plants appear primarily as necroses on leaf edges (marginal) and tips (terminal). Fluoride is accumulated in plants, damages leaves and inhibits growth.
Polycyclic aromatic hydrocarbons (PAH) are emitted primarily as incomplete combustion products, such as from internal combustion motors and heating plants. They also enter the environment as wash-outs from surfaces covered by tar, asphalt and bitumen. These substances are taken up by the human organism mainly by breathing, but also in food and by skin contact. The considerable carcinogenic and mutagenic potential of this group makes it more important for humans than for plants. Benzo(a)pyrene (BaP) is a leading component of polycyclic aromatic hydrocarbons.
Polychlorinated biphenyls (PCB) are ubiquitous in the environment today. Production of these chemicals was stopped in Germany in 1983, but considerable diffuse emissions continue from waste disposal sites, burning of waste-oil and waste, and leakage. PCBs enter the human organism primarily in the form of animal products, through accumulation along the food chain. Accumulation in plants seems to be of little phytotoxic significance. Great attention must be given to the exposure of the population to these substances, in view of their damaging effects on embryos and a well-founded suspicion of carcinogenic effects.
Polychlorinated dibenzodioxin (PCDD) and polychlorinated dibenzofuran (PCDF) are undesired side products of chlorine created in chemical and thermic processes. The main sources of emissions in Berlin are industrial (chemical cleaners, metallurgical processes) waste combustion plants, power plants, metal recycling plants, traffic, and domestic burning. Secondary sources are contaminated areas. The group known as “dioxins” accumulate in the food chain. They primarily enter the human organism in foods containing animal fats. The behavior of this material in the environment as well as its toxicity for human is not yet sufficiently known. Studies on these materials conducted for the Cadastre of Ecological Pollution Effects thus represent an important contribution to the environmental relevance of these materials in Berlin.
Bioindicators were also used to study the effects of highly volatile chlorinated hydrocarbons, photooxidants (ozone), and nitrogen oxides. These results are not presented, but can be found in the studies.
Maps 03.07.1 – .4 contain findings on pollution effects obtained by bioindicator use in Berlin since 1991. They are differentiated between 1) the determination of biological effects caused by a general complex of air pollutant factors working as a sum and 2) the analytical detection of specific pollutants.
The response of lichen to pollutants in the course of a “screening” program was the first indication for the presence of a pollutant load (Map 03.07.1). The Hypogymnia physodes lichen was employed for differentiation of small-area pollutant patterns in areas where a rich variety of natural lichen species can no longer exist (Map 03.07.2). Additionally, relevant pollutants were isolated with suitable accumulation indicators and evaluated for human toxicity, phytotoxicity, and ecosystem effects (Map 03.07.3/4).
This method enables integrated statements about general pollution stress over longer periods of time. Sulfur dioxide and dust were the primary urban pollutant components of stress factors on lichen in the past. Motor vehicle exhaust gases, ozone, and nutrient inputs are the relevant factors today. The dimensions of this influence can be measured by lichen.
A relationship has been detected between the specific community lichen existing at a site and degrees of air pollution. A rich variety of lichen species exists more frequently in areas with clean air. Both the number of species and the coverage are greatly reduced in areas with severe air pollution. There are even areas without any lichen cover at all. The absence of naturally appearing lichen in severely polluted areas limits the spacial differentiation of pollutant effects. This is why exposure monitoring methods are employed.
Lichen mapping for determining air quality is regulated in VDI Guideline 3799, Part 1. This ensures the general comparability of data. The evaluation of study findings do not allow any direct conclusions to be drawn about toxic influences on humans or plants. The evaluation can only serve as a point of orientation for general pollution load, especially if comparison with previous mapping shows an increase or decrease of lichen occurrence. An urgent need for improvement of air quality exists in areas determined to have “extremely high” pollution. These areas are characterized by occurrence of the toxic-tolerant crustose lichen Lecanora conizaeoides. In areas termed to be “severely loaded”, as indicated by the presence of this lichen, residents are at increased risk of respiratory illnesses (Rabe and Beckelmann 1987).
The foliose lichen Hypogymnia physodes was employed to determine the total effect of pollutants in study areas which have no distinctive natural lichen vegetation. The basic measure of effect given in VDI Guideline 3799 Part 2 is the mortality rate of the thallus (lichen body) at the end of the exposure period. It is not usually possible to draw direct conclusions regarding the amount of pollutant inputs based on the study findings, because SO2 and other factors affect the lichen. A general derivation from the mortality rate is that increased damages to other plant species can be expected, as well as a loss of species in the ecosystem, with increased effects on lichen.
Analysis of Pine Needles
The Scots Pine (Pinus sylvestris) is a widely distributed, native tree species in Berlin and Brandenburg. It is very well suited for long-term passive monitoring studies because it is an evergreen. Pine needles were sampled for the Cadastre of Ecological Pollution Effects because pine needles have good accumulation and response characteristics. Pine needles are exposed to prevailing pollutions all year-round, in contrast to the 14-day growth cycle of rye grass. The analysed elements characterize a longer period of time, thus integrating seasonal fluctuations of pollutions to an mean pollutant level. High winter SO2 inputs can be especially well studied by the sulfur concentrations of pine needles. Winter inputs cannot be determined by exposing rye grass in summer.
No binding evaluation basis exists for pollutant levels in pine needles. A comprehensive review of existing comparative studies was made in order to derive classification limits for “low”, “medium”, and “high” concentrations in the Berlin area. These value categories characterize the prevailing ecosystem pollutant level from airborne inputs and soil factors. They provide indications for the pollution load of the natural environment, such as forests, but they are not to be held equivalent with threshold value for the protection of cultivated crops or human health.
Standardized Rye Grass Cultures
Rye grass (Lolium multiflorum) is often used in agriculture as fodder (feed crop). It is an accumulation indicator representative for other food and feed crops and is often used for an estimation of load on natural vegetation. The grass is exposed during the growing season to register accumulation of airborne pollutants. Rye grass contents indicate if there is a danger of contamination in the consumption of plants and crops in the study area.
No federal German evaluation procedures exist. Comparative studies were used as a basis to develop guidelines for tolerance values below which there are no expected toxic effects on natural vegetation (cf. Scholl 1974), or for grazing animals or humans from contaminated plants by way of the food chain (cf. BGA 1986, FMV 1990).
Green Kale Exposure
Green kale (Brassica oleracea acephala) is a recognized standard plant for determining effects of organic airborne pollutants and is used routinely by local agencies. High frost tolerance allows it to be used in active monitoring during autumn and winter, when other plants cannot be exposed and airborne pollution increases. Green kale is especially suited for detecting organic pollutants because these pollutants are usually lipophilic (fat-soluble) materials and accumulate greatly in the leaf wax layer.
Procedures for breeding plant material, exposure, harvesting, scheme of evaluation, and analysis of test plants have been extensively established and tested (cf. Arndt et al. 1987; Rademacher and Rudolph 1994; TÜV-Umwelt Berlin-Brandenburg 1995). No limit or guideline values valid for all Germany exist for organic compounds in vegetable foodstuffs or feedstocks. The pollution levels “low”, “medium”, and “high” were defined using values found in other green kale studies in Germany. The defined classifications are an empirical aid. They do not consider toxicological aspects predominately. They allow only general indications of pollutant levels in reference to human health.