Hazardous Substances Thematic Assessment

The bow-tie diagram aligns with the DAPSIR narrative in the Thematic Assessment. Provisional confidence assessment: Medium (Medium Agreement on DAPSIR content + Medium Evidence to support connections) based on the approach described in Agreement 2019-02.

The bow-tie analysis for hazardous substances shows the relationships between the DAPSIR components which need to be considered in a cumulative effects assessment. Some Thematic Assessments have identified human activities which contribute to hazardous substance pressures that have the potential to contribute individually and cumulatively to biodiversity state changes. These Thematic Assessments concern:

Benthic Habitats ; Input of other substances:
Human activities can introduce a range of hazardous substances and pressures relating to increasing levels of contaminants in sediment (e.g., PBDE, PAH, PCB, metals, organotins), in biota (PBDE, PAH, PCB, metals, organotins, etc). These can lead to changes in state through effects on mortality, reduced breeding success and species fitness, or loss of most sensitive species (e.g., marine snails due to organotin).

Fish ; Input of other substances:
Synthetic substances and non-synthetic substances can cause physical harm to fish. Fish populations in freshwater environments face the most acute threat of chemical contamination, for example by metals, as a result of industrial or mining activities; these can lead to local population extinctions (Hamilton et al., 2016). In the marine environment, chemical contamination is a threat in coastal fisheries where pollutant levels are highest, particularly from oil run-off, production and transportation; petroleum; heavy metal contamination; and synthetic substances from agriculture and urbanisation (e.g., pharmaceuticals in sewage) (Hamilton et al., 2016). Food web transfer and bioaccumulation of pollutants in fish tissues (e.g., metals, persistent organic pollutants and organochlorine contaminants) can adversely impact fish in all aquatic environments in terms of reproduction, development and/or survival of offspring, and cause population declines (Hamilton et al., 2016).

Marine Birds ; Input of other substances:
In bird species, the input of other substances into their environment can cause contamination of the food web. Examples:

• Polybrominated diphenyl ethers (PBDE) contamination in biota can impact behaviour, learning and hormonal function. 
• Polychlorinated biphenyl (PCB) concentrations in biota can cause genotoxic effects, immune suppression, inflammatory response and endocrine effects. 
• Eggshell thickening leads to reduced hatching.
• PBDE and PCB both cause reduced reproduction and bioaccumulation in benthic, fish, bird and mammal species.

Marine Mammals ; Input of other substances:
Synthetic substances and non-synthetic substances can cause physical harm to marine mammals. Marine mammals are often predators at the top of the food web, and are sensitive to bioaccumulation, whereby toxic contaminants build up throughout the food web, with the highest concentration found in its top predators. Examples:

• PCBs can lead to reduced reproduction success or complete failure of the reproductive organs. Some contaminants in high amount can even cause death.  
• Mercury can cause the formation of cancer, decreased learning abilities and damage to the nervous system.
• Lead is highly toxic and can cause cancer and decreased learning ability.
• Cadmium can also cause cancer and further reduces bone strength.
• Other persistent organic pollutants, such as PBDEs, can be found in high concentration in marine mammals. While the decreased fecundity in those species has not yet been attributed to these substances, they have known effects on other species.
• These all potentially cumulatively impact the abundance, demography, and distribution of marine mammals.  

The State section describes the potential ecological impacts associated with hazardous substances in the marine environment. Input levels, frequency of occurrence, spatial extent, and exposure to different human activities all collectively contribute to the extent to which hazardous substances pressures are exerted on benthic habitats, fish, marine birds and marine mammals. To undertake a full quantitative analysis of cumulative effects requires consideration of the exposure pathways and ecological impacts. Further analyses and evidence of ecological impacts are required in order to progress the assessment of cumulative effects.

Hazardous substances can also combine with other pressures to collectively affect marine species and habitats. The assessment of cumulative effects is considered in the biodiversity thematic assessments ( Benthic Habitats , Fish , Marine Bird and Marine Mammal Thematic Assessments).