toxicology & forensics > The theory behind biological trace analysis

The theory behind biological trace analysis

A Spring Without Birdsong

von Prof. Dr Bernd Herrmann

In 1962, biologist Rachel Carson published her world-famous book “Silent Spring”, in which she warned of the consequences of inconsiderate use of DDT. DDT accumulates in the food chain and, thanks to its ­hormone-mimicking effects, causes serious damage to the organisms ­at the end of such food chains. One such effect is that the shells of many birds’ eggs become so thin that they break during incubation. The consequence: a silent spring without birdsong.

Natural awareness as a continuous process

The synthesis of organic compounds began more than 100 years ago: today, tens of thousands of these compounds can now be detected in environmental media (water, soil, air) all over the world. Such compounds have escaped into the environment through the production process itself, waste disposal or simple thoughtlessness. Via the food chain, some of these compounds induce severe clinical syndromes even in far-flung human communities. Compared to these, the runny nose now being experienced by some of our fellow humans due to pollen from spring blossomers like hazel and birch is fairly harmless. Those immune to hay fever may however end up being stung this summer for the first time by the Asian tiger mosquito – a recent European invader that can spread a whole host of dread diseases.

Beyond the philosophical aspect that life in general is lived exposed to the constant risk of hazards, these three examples do raise the question of whether – and how – such dangers can be forestalled. The first step is to monitor the environment. Many groups make such observations, from consumers and interested nature lovers to environmental researchers and the environmental monitoring institutions run by the federal and state governments.

Research scientist activities play the predominant role in such environmental monitoring, since the continuously maturing process of natural awareness is based on the strategies for problem determination and solution developed by basic research. These were also the first to even recognise the potential dangers. Since the three examples cited trigger biological effects, they fall within the remit of biological scientists: biochemists, physiologists or developmental biologists research the effects of DDT, pollen is analysed by botanists skilled in plant ecology, the tiger mosquito is identified by zoologists, while microbiologists describe the parasites that use this mosquito as a host or vector. Where research pursues the goal of environmental observation and hazard prevention, it is ascribed to “environmental monitoring”: alongside “forensic biology”, this is the second field within “biological trace analysis”.

Materials and effects in the spotlight

Biological trace analysis is an area of scientific research that observes and analyses biologically active substances, biological organisms and biogenic compounds or materials, so as to diagnose their mechanisms of action and use these to derive prognoses. Observation, analysis, diagnosis and prognosis are performed so as to observe, administrate and preserve the environment, and to avert dangers to human and other life or to materials. Unlike other fields of knowledge or scientific research, the establishment of biological trace analysis is a necessity backed by statutory law (German Basic Law (GG) ss. 2 and 20a, plus many other legal provisions and directives).

Biology and the environment

Environmental monitoring is a field within applied biology, and is the field with the greatest need for biologists drawn from the broadest spectrum of disciplines and the highest levels of specialisation. Such biologists test sugar beet pulp for residues of BSE prions from bone meal fertiliser, assess whether DNA from genetically modified organisms can escape into the environment, and verify that there’s calf in the calf’s liver pâté and that the Parma ham is from Parma. They investigate whether hormones from ovulation inhibitors can pass through waste water facilities into rivers, where they disturb sex ratios in fish, and they check bacterial loads in drinking water and hygiene in the hospital or catering sectors. They assess vermin affecting agriculture and forestry and how they can be ecologically controlled, whether the raccoon dog has crossed the River Main, how the salmon can be re-introduced and whether the cockchafer is still found around Darmstadt. They inspect goods from shipping or overseas freight to see if they carry pests, protected or invasive species, test returning holidaymakers for malaria, and establish which of our plant and animal species are under threat. And the list goes on and on. Lastly, they also recommend countermeasures, adjustments to tolerance ranges and the creation of nature reserves.

Biology and forensics

The epistemological principles for environmental monitoring are identical to those for the second area within biological trace analysis, namely forensic biology. Here, however, their implications are more direct. Forensic biology concerns itself with the examination of biological materials for the purpose of clarifying or reconstructing circumstances and events that form the subject of formal inquiries or investigations. The primary focus here is on investigating ‘traces’ in a narrower sense. Generally speaking, a ‘trace’ is material evidence of the former presence of an entity now absent. In the context of biological trace analysis, therefore, it is evidence that a living being was present. As a rule, this will be only parts of an organism – such as hair or saliva residues on cigarette butts – finger marks, etc. If a trace is to be first assessed on the basis of its material composition, this proves to be a highly problematic field of activity. Biological traces vary considerably in terms of their material composition (fluids, scales, hair, etc.), their species-specific origin (300,000 plant species, > 10 million animal species, ? species of microorganisms) and their state of preservation (fresh, degraded, fragmented, state dependent on media). Accordingly, their mere identification presents major challenges to the biologist’s expertise in the field of biodiversity.

No two traces are the same

In addition, three particular epistemological problems also arise. Firstly, a trace is the result of an event that is unique as to its historical and material nature – e.g. homicide with a knife. While there are many stabbings worldwide every single day, every crime is one of a kind: the time, place, motive, act and persons involved all differ. Since the event is unique, so too are the traces it produces. One-off events owe their allegiance to random chance and not the exigencies of regular processes. As one-time events, they themselves possess no recurrent structure. As a result, each trace is not just historically unique – but materially so. Furthermore, material qualities of traces also change local structures. Such changes follow empirical rules: by applying these rules, once can estimate the time a body spent lying on the grass from the degree of lightening shown by the grass leaves, for example, or examine a trail of blood in terms of drip patterns.

The second problem involves contextualising a trace – and this introduces an associated logical dilemma. At a crime scene, many traces will be present, yet not all are relevant to the crime, since some of them will stem from unrelated earlier events. From this overabundance of possible traces, only those with relevance must be recorded – i.e. placed in a crime-relevant context. This is possible only by advancing a hypothetical progression of events – yet it is precisely this that the trace analysis is supposed to establish. Initially, then, the possible contextualisation of a blood trail – whose drip pattern would fit the suggested progression of events – can only be provisional. Necessarily, one must perform subsequent molecular verification of the correlation of the blood trail to the victim, the perpetrator or uninvolved third parties.

This also broaches the third problem, centred on the “knowledge generating narrative” about the circumstances reconstructed by trace analysis. The term “drip pattern” already implicitly contains the description of a process. Such descriptions are founded on familiar, established scientific ‘best practice’ rules: “blood dripping from a blade will normally produce these kinds of drip patterns.” Knowledge-generating narratives are deployed in many ways within research, in situations where the general level of knowledge permits a sound description of historical events although eyewitnesses are unavailable. The most famous examples of such narratives are the ‘history of the universe’ or the ‘origin of species’. Each trace evaluation performed thus contributes to a knowledge-generating narrative about the progression of events. There is a danger, however, that such evaluations will embody persuasive tactics that hinge on the appraiser’s own opinion and are not founded on generally accepted methods of reasoning – or engage in speculation beyond that which can be reliably stated. Both intellectually and methodologically, forensic biology is thus one of the most demanding areas within applied biology.

Trends in trace analysis

In German-speaking Europe, biologists qualified in (crime scene) forensics tend to work at institutes of forensic medicine or criminal investigation departments; a few also work as independent experts. In Germany itself, there is a wide choice of degree and training courses focused on the environment, although fewer that address biological trace analysis. For forensic science itself, the degree and training courses on offer in Germany are entirely inadequate. If we consider the fact that the impressive methodological advances in lab techniques in particular are producing greater volumes of trace material – since this increases the prospects of successful trace analysis – and that internal security needs to be addressed long into the future, then there is a lack of relevant funding instruments. The University of Göttingen is one of the few institutions in Germany where expertise in trace analysis can be obtained during an MSc in Biology. To date, demand for this course easily exceeds the number of places available.

Literature
Herrmann B, Saternus K-St (2007)(eds) Kriminalbiologie. Biologische Spurenkunde, Vol.1. Springer, Heidelberg

Foto: CBS Photo Archive