Environmental soil testing

Understanding the quality of analysis

The importance of getting high quality analytical test results is not to be underestimated. Key decisions are made based on analytical data provided to the end user; however, how laboratories achieve and maintain quality standards and generate good quality data is often little understood.

It all begins with the sample submitted for testing. There are numerous standardised approaches towards environmental sampling – for example, BS ISO 18400 series, BS 10175, and BS EN ISO 5667 series. These standards also often reference sample handling and preservation. As such, much guidance is available to direct the sampler towards appropriate techniques and sample handling processes. However, it is unusual for accreditation to be held for such sampling, particularly in the contaminated land sector. As such the quality of sampling and the sample quality itself provided to the laboratory for testing may not be tightly controlled, leaving areas for doubt as to the integrity of the sample for testing and the appropriateness of the data generated.

Conversely, accreditation to testing standards is mandatory for laboratories to ensure fit for purpose testing methods are employed and high-quality data is issued to the customers.


BS EN ISO/IEC 17025:2017 – General requirements for the competence of testing and calibration laboratories is the testing standard of choice by many national accreditation bodies worldwide. In the UK, UKAS (United Kingdom Accreditation Service) is the sole National Accreditation Body. UKAS is recognised by Government, to assess against nationally and internationally agreed standards, organisations that provide conformity assessment services such as testing and calibration. Within the UK, there are additional testing requirements in relation to waters, soils and stack emission samples under the monitoring emissions to air, land and water (MCERTS) scheme from the Environment Agency which acts as a technical “bolt on” to BS EN ISO/IEC 17025:2017.

Environmental Soil Testing

Accreditation to these standards (BS EN ISO/IEC 17025:2017 and MCERTS) relates both to the overall quality management system as well as specific tests, providing an overall quality assurance framework for the laboratory to work within.

Key aspects of a Quality Management System

Quality assurance is a planned system of activities designed to ensure that the quality management system is effective. It is centred around what I like to call the four pillars of quality:

  1. Do what you say
  2. Say what you do
  3. Prove it
  4. Improve it

Following these simple statements allows the entire system to be navigated.

The following areas are mandatory requirements of BS EN ISO/IEC 17025:2017.

Impartiality and confidentiality

Testing and the staff involved in testing must be impartial (free from external influence) and be aware of the need to keep their work and the results of their work confidential between the laboratory and the customer. Staff are constantly reminded of these requirements and made aware of the necessity to disclose any conflicts of interest such that the influence of these can be minimised.

Structural requirements

The laboratory must be an accredited legal entity (or part of) and be responsible for the laboratory activities performed. Within the legal entity, an organisational and management structure shall be defined and active and effective at implementing and monitoring laboratory performance, including a continual improvement process.


Resource isn’t just about having the right equipment to do the job, it is also about ensuring laboratory capacity and capability meet the requirements of the customer and produce quality data that is fit for purpose. This is all encompassing – looking at the calibration of any equipment, metrological traceability, staff performing testing, the suppliers used, the overall facilities provided and the environmental conditions of the laboratory. Ultimately – without the appropriate resource, good quality analytical data cannot be generated.

Metrological traceability is a key aspect of reviewing laboratory resource and its ability to produce valid data. Metrological traceability is defined as “property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty”. This means that any result generated should have full traceability back to the International System of Units (SI). This may be through calibration of equipment by a competent laboratory; use of certified reference materials, which are provided by a competent producer (in the case of chemical standards, traceable to ISO 17034); or by the direct measurement of the SI units by comparison, directly or indirectly, with national or international standards.


Within the process requirements of the standard – there are many specific areas where it is important to document processes and follow such processes (Do what you say, Say what you do).

  1. Review of any customer requests for testing
  2. Selection, verification and validation of test methods
  3. Sampling
  4. Handling of items
  5. Technical records (Prove it)
  6. Evaluation of measurement uncertainty
  7. Ensuring the validity of test results
  8. Reporting of the results
  9. Managing complaints
  10. Handling Non-Conforming work
  11. Control of data and IT systems
Environmental Soil Testing

Of these, I will focus on items two and seven as key areas that it is important to consider and understand.

Selection and verification of test methods

Test methods can be selected from a range of published and recognised laboratory testing methods, or they may be developed in house by blending together knowledge and recognised testing methods, or they may be entirely developed in house. Recognised testing methods need to be verified as fit for purpose and effectively implemented by the testing laboratory. This verification ensures the test method meets the criteria defined in the standard method. Where the method is a simple physical test, verification may be through analyst competency audit, equipment verification or a combination of the two. Analytical test methods, particularly those with any aspect of in house documentation or development, will require a formal validation protocol to be followed with data meeting the required fitness for purpose criteria. A simple example of this can be found in MCERTS soils, which clearly states the method validation process to be followed. It also has performance requirements for a number of test parameters that must be met – namely specific precision and bias criteria.

In order for a test method to be granted accreditation, these requirements must be met and assessed to be fit for purpose by the accreditation body.

Ensuring the validity of test results

The requirements for ensuring the validity of test results are prescriptive and are often the most tangible when discussing with those unaware of laboratory quality management processes. This area details the processes to be followed to ensure the quality and validity of test results being produced. There is a lengthy list of criteria, not all of which will be applicable to every test method. However, the sentiment of all of these is that there shall be some kind of external verification of test results (certified reference material testing), as well as ongoing internal quality control such as equipment checks, testing of internal quality control samples, replicate testing, testing of blind samples, in addition to an overview and review of all testing results reported.

“reviewing proficiency testing data is an excellent way to get an indicator as to how a method or even the laboratory as a whole is performing”

Providing additional quality assurance on top of this is the requirement for laboratories to perform proficiency testing. Proficiency testing determines the performance of individual laboratories for specific tests or measurements and is used to monitor laboratories’ continuing performance.

Proficiency testing is also called inter-laboratory comparison. As this term implies, proficiency testing compares the measuring results obtained by different laboratories. In a proficiency test one or more test materials are sent around between a number of participating laboratories. Each laboratory carries out the testing according to a given set of instructions, performing their own test methods and reports its results to the administrator. The results reported by each laboratory for a parameter are compared to the reference value for that parameter. The reference value can be determined in various ways. The two most common ways are to use a reference laboratory or use the average of the values reported by the participants. Laboratories are assigned a performance score based on the result they produced in comparison with the target value and the standard deviation of the data. This will rate the performance of each test as acceptable, questionable or unsatisfactory. Any performance that is unsatisfactory must be investigated, whereas for questionable data it is good practice to investigate the results produced.

Reviewing proficiency testing data is an excellent way to get an indicator as to how a method or even the laboratory as a whole is performing. The samples are tested blind with no prior knowledge of the results, and the samples undergo the same treatment as commercial samples. In some industry sectors, the proficiency schemes and performance are mandated. This is the case for asbestos testing in the UK accredited by UKAS, whereby the participation in the AIMS scheme is mandatory.

Further management system requirements

There are additional requirements in relation to management system functions, which in the case of BS EN ISO/IEC 17025:2017 also meet the requirements of ISO 9001. Management system documents and all technical records shall be controlled and tamperproof (Prove it), and there are requirements specifically around improvements and corrective actions (Improve it).

Environmental Soil Testing

On the theme of improvements, laboratories must make an effort to identify any risks or opportunities for development. This theme of risk identification and mitigation should be embedded in any quality management system and is a defined consideration in any audit scenario.

“risk identification and mitigation should be embedded in any quality management system”

Each of the subject areas covered herein can be covered in significant detail, however, it is hoped that this overview gives a good snapshot of the requirements for maintaining quality in testing of environmental samples.