Methods for monitoring and control of environmental hazards (including food and water safety, atmospheric pollution and other toxic hazards, noise, and ionising and electromagnetic radiation) and cluster investigations

Bio-marker

Substances (molecules) used as indicators of a biologic state – i.e. as an indicator of normal or pathogenic processes or of biological response to an external agent.  Examples include: an antibody to indicate infection, a DNA adduct to indicate modification of genetic material or a protein that correlates with the risk or progression of disease.

Bio-monitoring (human)

Monitoring activities in human beings, using biomarkers (using biological samples), that focus on environmental exposures, diseases and/or disorders and genetic susceptibility, and their potential relationships.

Disease cluster

An unusual aggregation of health events that are grouped in space and time.

HACCP

Hazard Analysis and Critical Control Points – a systematic preventive approach to food and pharmaceutical safety that addresses physical, chemical and biological hazards as a means of prevention rather than finished product inspection.

Monitoring

The performance and analysis of routine measurements aimed at detecting changes in the environment or health status of populations.  May also imply intervention as indicated by monitoring data.

Post hoc

(Of an hypothesis) formulation after making the observation.

Surveillance

Ongoing scrutiny, generally using methods distinguished by their practicability, uniformity, and frequently their rapidity, rather than by complete accuracy.  Its main purpose is to detect changes in trend or distribution in order to initiate investigative or control measures.

Approaches to monitoring and control

For any potential environmental hazard one of the main principles for monitoring and control is to identify the critical agents, pathways and populations at risk.  Such considerations will guide the methods to be used for monitoring and surveillance.

Monitoring data

Monitoring (routine measurements aimed at detecting changes in the environment or health) can use data from a range of sources, including:

• Emissions inventories (records of the permitted or actual level of emissions from specified sources);
• Environmental data (measurements of the concentrations of pollutants in the environment);
• Bio-monitoring data (measurements of specific agents or their metabolic products in biological samples);Health data, which includes:-
  - Routine (surveillance) data;
  - Clinical surveillance (relevant to specific exposed populations);

Relevant health data might include:
-    infectious disease monitoring data;
-    health care utilisation data (hospital admissions, primary care consultations);
-    births, congenital anomalies and related data;
-    cancer registrations;
-    mortality statistics;
-    epidemiological surveys.

Epidemiological surveys are usually undertaken for research purposes rather than as part of monitoring, but periodic surveys may provide useful evidence about biological uptake and effects (bio-markers from clinical specimens, indicator diseases states).

In general, the control of environmental hazards depends on:

(i)     defining acceptable levels of exposure and hence health risk (or taking a precautionary approach in the absence of clear evidence);
(ii)    determining the levels of control needed to keep exposure below the specified thresholds.

Such assessment usually takes account of toxicological and epidemiological evidence, and evidence on exposure pathways, environmental persistence, bio-accumulation, etc.

Control measures

A range of methods of control may be applied, including:

• Licensing / banning specific substances (e.g. CFCs);
• Setting of emissions controls (e.g. vehicles exhausts, industrial emissions);
• Enforcement of concentrations or exposure limits for specific target groups (e.g. radiation workers);
• Enforcement of health and safety protection (e.g. for workers handling biological agents).
• Setting of guidelines/standards relating to environmental levels (e.g. air pollution monitoring)

These may be implemented by voluntary agreement, balance of penalties and benefits to encourage good practice and dissuade bad, legal mandate.  Measures which entail licensing, emissions control, or health and safety protection, can be enforced on individuals or individual companies.  Guidelines and standards relating to general environmental levels do not entail direct influence over the polluters.

Water and food

Quality standards are set for the physical, chemical and biological characteristics of drinking water and monitored throughout the water treatment and distribution network through to the household tap[1].  Among the range of tests and specified limits are those relating to pH, microorganisms including marker agents such as faecal coliform bacteria (E coli), Cryptosporidium and Giardia lamblia, chlorination by-products, dissolved metals, salts and metalloids (lead, mercury, nitrates, arsenic, etc.), organic matter and radon. 

Biological and chemical testing is also carried out in the food industry, where, as with water safety, the approach is typically based on the principles of the Hazard Analysis and Critical Control Points (HACCP), which seeks to identify potential hazard points, so that key actions, known as Critical Control Points (CCP's) can be taken to reduce or eliminate the risk of the hazards being realised. The system is used at all stages of food production and preparation processes including packaging, distribution, etc[2].

Air pollution

The quality of air has long been recognised to affect respiratory health. Burning fossil fuels not only produces CO₂, promoting global warming, but also other by-products of combustion, NOx, SO₂, CO, Particulate matter. WHO guidelines exist to limit outdoor air quality in urban areas[3], but also more recently the health burden from indoor air prompted limits from biomass burning in domestic settings[4]. Europe set a series of directives to target poor air quality[5], which member states implemented in national air quality strategies. The cornerstone of the UK strategy to meet air quality objectives is the system of Local Air Quality Management[6], introduced in the 1995 Environment Act[7] .  UK Local authorities are required periodically to review and assess the current and likely future air quality in their areas against national air quality objectives[8] for seven air pollutants included in regulations for that purpose. Where any objective is unlikely to be met by the relevant deadline, local authorities must designate those areas as air quality management areas (AQMAs) and take action, along with others, to work towards meeting the objectives. Local measures may include:

• work with relevant authorities responsible for highways and/or environmental regulation on possible emissions reduction measures;
• local traffic management schemes, including use of low emission zones and congestion charging in some areas where appropriate;
• commitment to developing or promoting green travel plans and/or to using cleaner-fuelled vehicles;
• information dissemination to the public;
• promotion of sustainable and healthy transport such as walking and cycling;
• partnerships with bus or fleet operators to deliver cleaner, quieter vehicles in return for better bus lanes or more flexible delivery arrangements.

Noise

Noise is a complex exposure, as its effects on health and well-being are a function of multiple parameters, including: its intensity, its duration, its intermittency, its nature and quality, and its origin[9].  Loud noise may cause deafness, but constant background noise (e.g. from heavy traffic) is often tolerated better than intermittent noise from a neighbour.  The nuisance value of noise is more than just the level of sound, and the sources of noise that is most often the source of complaints is neighbours.

Health effects of noise pollution are increasingly documented and controlled[10], [11]. In implementing the EU’s Environmental Noise Directive[12], the UK’s Department of the Environment, Food and Rural Affairs (DEFRA) generated noise maps to provide an overview of the ambient noise climate in cities and major transportation sources in England[13].   The Noise Policy Statement sought to reduce noise exposure through management and land use planning[14].

Ionising and electro-magnetic radiation

Monitoring and protection against radiation risks covers a number of important areas:

• Some governments recommend that households in high radon areas have radon monitoring carried out for a test period of three months[15].  There are various engineering solutions available to reduce levels if found to be above the action limit of 200 Bq.m^{-3 [16]}.
• Workers in the nuclear industry, or in other fields where there is exposure to ionising radiation (e.g. medical imaging), are required to wear radiation badges to monitor personal exposure. Removal from further exposure is required if a personal dose limit is reached[17].

For non-ionising radiation sources, there are published guidelines on exposure limits to static magnetic fields and to time-varying electric, magnetic and electromagnetic fields (up to 300 GHz)[18]. The guidelines advise basic restrictions to provide protection against the established adverse health effects of exposure, e.g shielding or limiting frequent use (e.g. mobile phones).  

A disease cluster implies any unusual aggregation of cases of illness or disease that are grouped in space and time.  The concept is somewhat complicated, however, because it begs the question of what is ‘unusual’?

The issue often arises that someone notices an apparently high number of cases of disease in a particular street or locality, and wonders whether there might be a connection with a local environmental problem.  But in such circumstances it is very difficult to interpret the significance of the observation, as the cases may reflect no more than normal variation or randomness in time and space.  The difficulty lies in the fact that the hypothesis of an unusual level of disease occurrence is formulated after seeing that there appears to be a high number of cases.

A formal statistical test might indicate a higher than average number of cases locally but that should not be surprising as the only reason one is looking is because someone has noticed that there does appear to be more cases than usual.  But it may be no more than a chance occurrence.  The difficulty is that the hypothesis of a ‘cluster’ is post hoc – developed after the observation – and therefore almost impossible to interpret appropriately.

Because of this most epidemiologists realise that there is usually very limited scientific and public health value in investigating the majority of observations of disease clusters.  These arguments were very well articulated by Rothman (1990)[19], who concluded that:

1. With very few exceptions, there is little scientific or public health purpose to investigate individual disease clusters at all;
2. There is likewise very little reason to study overall patterns of disease clustering in space-time; and
3. As a consequent of points 1 and 2, no statistical methodologies are needed to refine our study of disease clusters or clustering in general.

And indeed, in practice it has been found that very few cluster investigations ever reveal an apparent underlying environmental cause (Goodman et al 2012).  Most such investigations are inconclusive.

However, it is recognised that apparent disease clusters do have to be taken seriously, if only to allay public concerns, and various proposals and guidance have been made about staged investigations that only lead to formal epidemiological studies when the case appears very strong (CDC, 1990).  The debate about when to proceed has been summarised by Neutra (1990) in a response to the Rothman paper (reference given below). Many countries have developed and published staged guidance for the investigation of clusters of non-infectious diseases. A staged approach allows the opportunity to collect data specific to each stage and make a decision whether to continue the investigation further or terminate it.

Countries that have developed guidance include the US, New Zealand and the Netherlands (websites below). The WHO currently has guidance in development which will be available shortly.