Mercury in the fish of Cazaux-Sanguinet lake

High amounts of mercury have been identified in fish from the lake. This highly toxic heavy metal can lead to deregulation of the central nervous system, especially for children and pregnant women.

From 2008, the San conducted several analyses of fish samples, searching for possible traces of heavy metals, PCBs and dioxins. These analyses revealed the significant presence of mercury in fish flesh.

Analyses 2008 – Pike

These analyses were carried out on a pike caught in early June 2008 in the Bay of Ispe (Lake of Cazaux-Sanguinet). The preparation of the fillets was made by the SAN following the recommendations of the “Ad scientifique” laboratory. The analysis was performed by “AD Scientifique”, a laboratory empowered by IPRP (Intervenants Prévention des Risques Professionnels) for technical and medical fields, certified by the Ministry of the Environment.

Summary of results
Mercury 0,84 1 µg/g
Dioxins and furanes 0,25 4 pg/g OMS-PCDD/F TEQ
PCB 1,18 4 pg/g OMS-PCDD/F TEQ
(*) european regulation CE 466-2001 et CE 2375-2001.

Analysis 2009 – Eel and Perch

to check whether the high mercury content is specific to the fish we analyzed in 2008 or common to all the fish in the lake, the mercury was searched for in an eel and a perch. The results are as follows:

Eel(562g, 61cm) 0,4 1 µg/g
Perch (900g, 40cm) 0,26 0,5 µg/g

If mercury levels remain below the European standard, they are nonetheless high and worrying, particularly for pikes (at the end of the food chain predators and therefore strongly impacted by the bioaccumulation phenomenon).

Analysis 2012 – Pike

Pike (1200g, 62cm) 0,06 1 µg/g

The mercury concentration is low but this is a relatively small pike.

Analysis 2014 – Pike

Pike (1500g, 67cm) 0,06 1 µg/g

The mercury concentration is low but this is a relatively small pike.


Here is an interview with the president and secretary of the San completed late 2009 (courtesy of FR3 Aquitaine).

What is Mercury?

Metals are natural substances found in the soil in the form of ore. Many metals are indispensable to living organisms but can become toxic at high doses. Unlike organic substances (like most pesticides), metals cannot be degraded into less toxic substances. Although there is no strict definition, a metal is generally considered heavy when its density is greater than 5. Mercury is one of the most toxic metals, notably ranked 3rd, behind Arsenic and lead, in the in the top 20 toxic substances established by the ATSDR (Agency for Toxic Substances and Disease Registry, see It is commonly used in different industries: for example, it is used for the manufacture of batteries, lamps, contactors …, in ammunition for hunting or military activities, as a catalyst and pigment in the chemical industry, as a measuring apparatus or for the manufacture of fungicides. It can be absorbed by inhalation of vapors or ingestion of mercury compounds. Skin contact contamination is more rare.

Most acute poisonings are due to elemental mercury (metallic) heated and converted to mercury vapour. Indeed, it is poorly assimilated by ingestion while it is very active by inhalation. High concentrations of mercury vapour cause coughing, shortness of breath, chest pain, pulmonary edema and, in the most severe cases, death by respiratory failure. In less serious cases, the harmful effects will also affect the nervous system with onset of tremors, kidneys and the digestive system.

For its part, the chronic toxicity of mercury will include persons exposed to low-concentration mercury vapours for a long period of time, generally for professional reasons. The intoxication then acts mainly on the central nervous system. It causes the “Mad Hatter’s Disease” (the mercury nitrate was used in the past for the manufacture of felt hats): tremors, lack of coordination of movements, changes in behaviour. When Mercury is present in the environment, it is transformed by micro-organisms into organic mercury. Methylmercury is the most dangerous of organic forms because it is very stable and it is very high bioaccumulation in living organisms. Methylmercury acts mainly on the nervous system, but the kidneys and eyes can also be affected.

Risks and recommendations related to fish consumption

The toxicity of fish or shellfish is different from that of water. Indeed, not only we do not consume as much fish or shellfish as water, but the concentration of toxic products also differs. This difference in concentration is explained by a phenomenon called biomagnification or bioaccumulation that corresponds to the increase in concentration of toxic products in the tissues of an animal relative to the environment in which it lives (uses for aquatic animals). The ratio of the two concentrations is BCF (bioconcentration factor). Thus, as fish consumption is lower than that of water, only substances with BCF greater than 20 (and primarily those with BCF greater than 1000) will have a more dangerous concentration in fish than in water. This is particularly the case of Mercury, the BCF of which is about 9000. Many measurements of mercury, carried out at Lake St. Clair (Canada), showed a near proportionality between fish size and mercury concentrationt (cf. UNEP, World Mercury Assessment, 2002). The species of fish that also have an influence.


: UNEP, global mercury Assessment 2002, p94, Lake St. Clair (Canada).

The FDA (Food and Drug Administration) provides the following advice based solely on mercury levels: for pregnant women and young children.
-Do not eat tilefish, shark, swordfish and king mackerel as they contain too much mercury.
-Eat up to 12 ounces (about 340gr or 2 average servings) per week of different fish or seafood that contain less mercury.
-Check local recommendations for fish caught by family or friends in local lakes, rivers and coastal areas. In the absence of any recommendations, do not exceed 6 ounces (average serving) per week of fish you take but do not consume other fish during this week.

The presence of high-dose mercury was revealed on another lake on the Aquitaine coastline. This is the Carcan Hourtin lake, for which a Prefectural decision was issued on July 19, 2012, banning the consumption of fish from the lake.