Bioaccumulation of mercury in muscle tissue and hepatopancreas in red crayfish (Procambarus clarkii) in a transect of the Valdeazogues river and tributaries, Almadén Hg mining district, south central Spain.

The Almadén mercury mining district, located in South-central Spain, has been the most important producer of this element worldwide, until the cessation of exploitations in year 2003. The environmental consequence of this activity affects an area of some 250 km², coincident both with a geological structure (the Almadén syncline) and a river basin (the Valdeazogues river and tributaries). The old cinnabar (HgS) mines and mineral showings are scattered in the syncline and in the basin, favouring a wide distribution of the elements in the soils and sediments, as reported by previous publications from this research group and partners.

Crayfish (Procambarus clarkii) is an exotic river crab, with has replaced the autochthonous one  (Austropotamobius pallipes) due to its voracity. It is very common all along the Valdeazogues river and tributaries, and it is captured and consumed by local population in summertime, when it is easily captured in the ‘tablas’, water accumulated in river pods during the cessation of water running due the stational drought. Preliminary data on the Hg contents in this species, obtained in year 2005 reach up to 9,060 ng g^-1 (in muscle) and 26,150 ng g^-1 (in hepatopancreas), according to some previous publications of this research group.

In this communication we present new data on this issue, obtained during the year 2022 along the Valdeazogues river and in some of its tributaries. In this research, 330 crayfish (sizes between 7 and 12 mm) were captured from upstream of the El Entredicho open pit mine to downstream of the confluence with the Guadalmez river (about 36.3 km), as well as the Los Álamos stream, and the Azogado stream, both tributaries of the Valdeazogues. All specimens were analysed by Zeeman effect atomic absorption spectrometry.

The overall results showed maximum values of 3,567 ng g^-1 of total Hg in muscle tissue, with a mean value for the district of 1,617 ± 920 ng g^-1. In hepatopancreas which is an organ of the digestive tract with functions of absorption and storage of nutrients, as well as synthesis of digestive enzymes, the maximum value is very similar: a maximum of 3,590 ng g^-1, while the mean is slightly lower, 1,025 ± 1,028 ng g^-1. For the whole population, the relationship of Hg content in muscle tissue and hepatopancreas with size is not appreciable, probably because they are organisms of fast grown, and there is no general relationship between age and size. On the other hand, there is a relationship between Hg in hepatopancreas and salts contents and total Hg concentration in the nearby sediments.