Introduction to risk assessment

A risk assessment is the result of combining a hazard assessment with exposure scenarios – risk is a function of hazard and exposure.  To put it very simply:

Non-hazardous and low exposure = low risk

Non-hazardous and high exposure = good hazard assessment required

Hazardous and low exposure = risk management required

A hazard assessment needs to consider the physico-chemical, toxicological and ecological properties of a chemical substance and the result of this assessment leads to Classification with assignment of  ‘R Phrases’; however, this does not reflect the risk of the materials to workers, consumers or the environment and to take the hazard data to the next stage of assessment, it is necessary to understand potential exposure.

Risk assessment principles

A risk assessment to meet the requirements of Directive 93/67/EEC (as described in its associated Technical Guidance Documents), is currently expected for new substances being Notified or for high-volume high-risk ‘existing’ substances being reviewed under the existing chemicals regulations.  However, REACH will require the need to perform a risk assessment on virtually all substances being supplied over 1 tonne in the guise of a ‘Chemical Safety Report’ (CSR). 

Even without the need to meet regulatory requirements, ‘risk assessment’ is an essential part of responsible care during the production, supply or use of any chemical material.  A basic risk assessment will help determine what conditions to avoid or what protective equipment to recommend to meet statutory requirements for handling chemicals – such as the communication or risk to customers, protection of workers and also to minimum impact on the environment through loss or accident.  The Safety Data Sheet (SDS) itself is a product of a risk assessment in that it describes how to reduce exposure in accordance with known properties of the material. Under REACH, the SDS will need to take into account elements of the CSR.

Any type of risk assessment should include consideration of:

·        The life cycle of the product

·        Potential hazards to health and the environment

·        Physical form (solid, powder, liquid, gas etc)

·        How is the product handled (manually, automatically)

·        Is there contact with workers / consumers

·        Is there a chance of loss to the environment

·        What happens to the product after use (disposal)

The conclusions of a risk assessment is to compare the estimated exposure with the estimated effects; for the environment, this is expressed as a PEC / PNEC, based on the ratio of predicted environmental concentration (PEC) and predicted no effect level (PNEC).  Human health elements to the risk assessment are less clear-cut in their conclusions, but the principles remain the same with a comparison between the predicted level of exposure and the known or estimated degree of hazard.  The Derived No-Effect Level (DNEL) is estimated from toxicity data with the application of safety factors.

The environment

The Predicted Environmental Concentration (PEC) is based on models for the degradation or distribution of the substance in the environment (between water, air and solids) using physico-chemical and biodegradation data.  As well as the test data, other key factors include how the substance is manufactured, formulated or used and the dilution factors from use. 

The distribution of chemicals discharged to waste water treatment plants is described in the aptly named ‘SimpleTreat’ model.  This is a simplistic model that considers the volatility (Henry’s constant, H), the partition coefficient, adsorption coefficient and biodegradation.

Volatility                         Log H > 3           = Significant loss to air

Partition coefficient         Log Kow > 3      = Accumulation threat

Adsorption Coefficient    Log Koc > 3       = Adsorption to soil / sediment

Biodegradation               > 60%                 = Biodegradable

The model, presented in tabular form in the TGD or incorporated into the software of the risk assessment model EUSES (see below), compares each of these factors in determining the distribution of the substance in the environment.  A water soluble substance with Kow = 0, that is biodegradable, for example, is predicted to be 76% degraded with 24% lost to surface water.  But a non-biodegradable poorly water soluble material with a Log Kow of 4, may have 56% to water and 44% to sewage sludge.

Default figures are provided in the Technical Guidance Documents (TGD) for Directive 93/67/EEC, describing estimated concentrations of waste in effluent, standard dilution factors, sizes of water treatment plants etc. These default values consider worse-case scenarios with, for example, 2% of material produced being lost to waste water, the position of the production unit in a small town with a small treatment works, and with final discharge going into a small stream. However, where only limited sites are involved in production, formulation or use, location-specific factors can be used, such as the size of the waste treatment works, river flow rates etc.  and this can make a big difference to the final conclusion.

The Predicted No Effect Concentration (PNEC) is based on environmental effect data, such as toxicity to fish, Daphnia or algae and is determined by applying a safety factor. For acute studies, the safety factor of 1000 is applied to the EC₅₀ value; ie. a Daphnia EC₅₀ following 48 hours exposure of 50 mg/l would lead to a PNEC of 0.05 mg/l.  Longer-term studies require a smaller safety factor, as indicated below; 

Acute EC₅₀           ÷ 1000   (Acute = short term, eg 4 days fish)

Sub-acute EC₅₀  ÷   100   (Sub-acute = medium term, eg 21 days fish)

Chronic EC₅₀      ÷    10    (Chronic = long term, pond work etc)

In the absence of effects with acute studies, the PNEC is set at 1/1000 of the limit of solubility; likewise if there are no effects in longer-term studies, the PNEC will be 1/100 or even 1/10 of water solubility.

The ratio between PEC and PNEC is ultimately used as an indicator of risk, allowing it to be quantitatively labelled.  If the PEC is greater than the PNEC (ie. ratio > 1 ), then it can be assumed that there is a risk of effects to the environment.  The scale of the risk can therefore be crudely measured by considering this ratio – a figure of 1 to 10 is of low concern, but over 100 is of major concern, and limitation of supply could be required. 

Conclusions under the current Directive are:

1          PEC / PNEC < 1         = No immediate concern

2          PEC / PNEC 1 - 10     = Of concern if supply volumes increase

3          PEC / PNEC 10 - 100 = Further data required

4          PEC / PNEC > 100      = Reduce risk immediately

(Note EUSES refers to PEC/PNEC is referred to as Risk Characterisation Ratio ‘RCR’  )

Human exposure

A risk assessment based on human exposure should consider the type of exposure; whether deliberate or accidental, whether repeat or one-off or whether direct (eg. factory workers) or indirect (eg. in food or drinking water).   The physico chemical properties such as dusts, vapours or liquid inhalation, splashing must also be considered as this can effect exposure routes.  Physical hazards, such as flammability or explosivity are also important for overall risk considerations. 

Quantifying exposure is very difficult and models attempting to make this easier (such as the EU model, EASE) rely on inputs such as vapour pressure, temperature of the process leading to exposure, dust content etc.  Other than the rather simplistic model EASE, the finer points of human health risk assessments should be left in the hands of an expert.

In an attempt to quantify ‘safe’ levels for human exposure, it is necessary to calculate a Derived No-Effect Level (DNEL) that is based on safety factors being applied to toxicity data endpoints such as the lowest observed adverse effect level (LOAEL) or no observed adverse effect level (NOAEL).  The DNEL effectively follows the same principle as the PNEC for environmental effects.

Exposure needs to be considered in details in the Exposure Scenario (ES) that is part of the risk assessment process.  The content of the ES is not much more than would currently be provided in a risk assessment for new substances, but is a more formal assessment.  It is also designed to be more specific to particular uses or processes and different processes will require separate ES.

Human exposure

A risk assessment based on human exposure should also be considered.  This will depend on the type of exposure, whether deliberate or accidental, whether repeat or one-off or whether direct (eg. factory workers) or indirect (eg. in food or drinking water).  

Although the Technical Guidance Document for Directive 93/67/EEC does devote a large proportion of its pages to human health risk assessment, there is little direct support for those preparing risk assessments and there is no simple quantitative assessment as found with environmental data.  Instead, it is necessary to make a full review of all parts of the life-cycle in which the substance can come into contact with people, including manufacture, transport, storage, formulation, use and disposal.  Parts of the life cycle may not  be obvious, such as the exposure to pigments caused by the degradation of paints.  The exposure during manufacture of a pigment or its formulation into paint may seem obvious, as is the exposure to the wet paint when applying it to a surface.  However, the exposure to the paint from weathered surfaces is less obvious, but it all needs considering.

REACH introduces the concept of the ‘Derived No Effect Level’ (DNEL) that tries to quantify the no effect concentration for human exposure.  This is more complex than the Environmental PNEC (see above in that it considers inter-species reliability as well as the end-points assessed.

The table and notes below are taken from draft RIP document on Risk Assessment that sets out the preliminary Technical Guidance Document (TGD)

Default assessment factors

a             AS = factor for allometric scaling (See TGD TC for further details)

b             Caution should be taken when the starting point is an inhalation or diet study (See TGD TC for further details)

c             Not always covering risk characterisation of very young children (See TGD TC for further details)

d             See TGD TC for further details for deviations from default

e             This applies to systemic effects; for local effects in general no AF for differences in duration is to be applied (since the effects are often concentration- rather than dose-dependent). Also, the AF for intra-species differences should be the same for workers and the general population (i.e., for both populations a default value of 10) because no difference in sensitivity for local effects is assumed between these two populations. Hence, one DNEL for local effects is set which can be applied to workers and the general population.

Until agreement of the TGD, the simple ‘tier I’ assessment factor AF 1200 should be applied unless there are reliable long term data (eg Carcinogenicity) or data on a number of species, especially non-rodent.  In reality, most substances being assessed under REACH will not have this level of data and the default factor will probably apply.   Applying AF 1200 to the 1000 mg/kg/day 28 day toxicity rat study will lead to a  DNEL of 0.83 mg/kg/day

Risk assessment software

To help users of chemicals, software can be obtained from European Competent Authorities (such as the UK HSE).  Programs include EASE for making a simple assessment of worker exposure and EUSES for predicting environmental impact. 

EUSES is quite complex to use and interpret and can be manipulated to give a more realistic answer than if it is used at its most basic level, using pre-set defaults.  For example, simple changes can be made to change the size of waste water treatment works or to put in the correct local dilution rate when effluent finally reaches surface water in the environment.  It is also possible to make changes to more subtle parameters that only environmental chemists can fully understand – or at least, they claim to be able to.

Communicating Risk

The communication of risk to customers is through the SDS and where appropriate, the Exposure Scenario.   Even though substances over 1 tonne supply will need to be considered with an exposure scenario, lower volume hazardous substances will still require an SDS in the same way as currently applies.

The CSR does not need to be given to customers, but the ‘enhanced’ SDS must take into account the conclusions in considering risk reduction recommendations. 

Preparing a CSR

The precise format is still open for discussion, but the technical content of the CSR is effectively the same as the current risk assessment requirements.  However, it is proposed that the CSR will be prepared in two parts; Part A is the conclusions and declarations that risk management measures are implemented and communicated and Part B that is the main technical component.

Part B needs to consider:

1          Identity

2          Manufacture and use patterns

3          Classification and labelling

4          Environmental fate assessment

5          Health hazard assessment

6          Physical hazard assessment

7          Environmental hazard assessment

8          Assessment of whether PBT* or vPvB

9          Exposure assessment

10        Risk characterisation

* Persistent Bioaccumulative Toxic or very Persistent, very Bioaccumulative

The main source of hazard data will be the Chemical Safety Assessment (CSA) and the format for this will consider the environmental hazard, the human health hazard and physico-chemical health hazard data as well as the vPvB potential.  If vPvB, additional elements will need to consider exposure assessments and risk characterisation; if vPvB, close control over supply is expected and it is possible that Authorisation will not be given.

Exposure Scenario (ES)

The CSA needs to be considered in the light of the ES and the resulting comparison will provide the key to the risk assessment – comparing hazard and exposure.

To prepare the ES, suppliers will need to liase closely with their customers to ensure that the scenario for exposure is realistic and conversely, once prepared, the user must not deviate from conditions used for the ES.  For specialist uses, or if the use is considered confidential, the user will need to prepare an ES and perhaps even a new CSR to cover their particular use.

The communication of exposure data up and down the supply line is anticipated to be one of the more difficult activities facing industry.  There are perceived to be many problems concerning confidentiality and data ownership, but only industry can find answers to the communication problems.  Downstream users (DUs) can provide their own ES and CSR, but will need to report to the European Central Agency these uses in case the Registration of the substance is itself compromised and new Authorisation is required.

Technical Guidance Documents

Draft technical guidance documents have been prepared under RIP 3.2 (REACH Implementation Project) and are published by the ECB (http://ecb.jrc/documents/reach).  More guidance is expected over the coming months.

SDS Communication

The format of the SDS will change under REACH, but the basic 16-point format will remain.  However, the findings of the ES and CSR need to be communicated in various section of the SDS and it is important that the risk reduction recommendations are consistent with the ES and CSR. 

The ES may also need to be supplied to the customer to provide more detailed information on safe handling and control.  Sections relating to physico-chemical properties, toxicology and ecotoxicology must also be consistent with the CSA that in turn has been used to prepare the CSR.

Effectively, the job of the SDS remains the same, but under REACH, it is expected that there will more information to communicate at a greater level.  Chemical supply may also be linked to specific uses only and the SDS must obviously make this clear.

For the vast majority of non-hazardous products, there may be little real change in communication requirements.   

Control and Authorisation

Dangerous substances may be authorised only for specific uses that have been considered to represent an acceptable level of risk or are considered to be of socio-economic benefit for a specific function.  Restrictions on Authorisation can be expected on substance considered to be CMR (Carcinogenic, Mutagenic or Toxic for Reproduction) or are PBT or vPvB.   It is possible that total restrictions are placed on certain substances, as is currently enforced through specific Directives.

For all hazardous substances, some level of risk management will be required and this is to be proposed in the CSR and communicated through the SDS and ES.

Conclusions