In 2012, the ICES Study Group on Integrated Monitoring of Chemicals and their Effects provided a framework for integrated monitoring to the OSLO-Paris Commission. UNEP/MAP and HELCOM expert groups have also developed guidelines on integrated monitoring of chemicals and their effects for the Mediterranean and Baltic Sea. This document provides the technical information for one of the biological effects measurements, the lysosomal membrane stability (LMS), which is a part of the above mentioned integrated monitoring approaches. Lysosomes are cytoplasmic, single membrane organelles whose condition is sensitive to stress whether it be due to environmental conditions or exposure to a wide array of contaminants. Two different methodologies have been developed to assess LMS in mussels: an enzyme cytochemical method using cryostatic sections of digestive gland tissue, and an in vivo cytochemical method (using haemolymph cells). In this document, different aspects of the operational procedures have been standardized and harmonized, with particular reference to the in vivo cytochemical method. New graphical material has been added to clarify criteria of interpretation and new external quality assurance programmes for measurements of lysosomal membrane stability have been proposed. Background (BAC) and environmental (EAC) assessment criteria to assess the LMS data are provided. Additionally, a new scoring procedure to enhance the sensitivity of the LMS measurements using the in vivo assay is provided.

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