Contamination parasitaire des sédiments marins. Étude sur le site de Barcelone Parasitological contamination of marine sediments. Study in Barcelona area

Résumé

Les apports contaminants d'origine continentale jouent un rôle fondamental dans le processus de contamination du milieu marin. Une étude a été réalisée sur le site de Barcelone, afin de réaliser un inventaire des sources de pollution et de déterminer l'influence de ces apports sur la contamination des sédiments marins; ce lieu d'expérimentation ayant été retenu du fait de la multiplicité des types de rejets effectués en mer : eaux usées, boues de station d'épuration... Les sédiments ont été prélevés à partir du navire océanographique au cours de 3 campagnes de novembre 1987 à juin 1988 à des distances de 50 mètres à 4 km de la côte et à des profondeurs de 10 à 52 métres. Globalement 88,8 % des échantillons analysés renfermaient des oeufs d'helminthes (Nématodes et/ou Cestodes) à des concentrations variant de 5 à 256 oeufs 100 g^-1 de sédiments Si des oeufs de Nématodes (Ascaris, Toxocara, Trichuris, Capillaria) sont retrouvés dans tous les échantillons positifs, seulement 44,4% renferment des oeufs de Cestodes (Taenia, Hymenolepis). Chez les Nématodes, les oeufs de Toxocara ont été retrouvés avec une très grande fréquence (66,6 %) chez les Cestodes des oeufs de Tenia (38,8 %) prédominent Il faut donc noter la moindre résistance des oeufs de Cestodes dans le milieu marin. Quant à la viabilité réalisée sur les oeufs d'Ascaris, elle s'échelonne selon les prélèvements de 5 à 100 %. Des études ultérieures devraient être poursuivies pour vérifier si ces oeufs viables ont encore conservé leurs potentialités infectieuses.

Mots-clés:

• Eaux usées,
• boues de station d'épuration,
• oeufs d'helminthes,
• Nématodes,
• Cestodes,
• sédiments marins,
• viabilité,
• Ascaris

Abstract

Microbiological pollution of the marine environment is often the result of man's presence in the coastal zone (offshore flow of sewage sludge or effluents from raw or treated wastewater).

Although many studies have been carried out on the viral and bacteriological pollution of the marine environment, very little is known about parasitological contamination of this important resource. This investigation is aimed at the problem of parasitological contamination by examining its sources and their effect on the contamination of marine sediments of a specific coastal region.

Barcelone was selected as the study site because of the many types of effluent flowing into the sea. These are due to : two highly polluted rivets (the Besos river and the Llobregat river), treated and raw wastewater. Sewage sludge is transported offshore front Barcelone through a deep conduit.

Marine sediments were collected at distances between 50 m. to 4 km of the shores of urban Barcelone at depths varying from l0 to 52 m. Samples obtained by the oceanographic vessel « Garcia del Cid » required use of a Reineck device.

Parasite density was too low for direct microscopic examination, thus all the samples underwent an enrichment procedure. A preliminary study had shown that, out of all the various concentration methods available, the one described by Janeckso-Urbanyl was the best adapted 10 the samples investigated here. This method uses a high density (d = 1.44) potassium lodomercurate solution with low viscosity so that the eggs rise rapidly to the surface. The slides were enlarged 100 times and numbered with a Mac Master slide. The determination of the viability of Ascaris eggs was studies after a n-butanol treatment. The results are expressed as number of eggs per 100 g-1 sample.

Helminth eggs were found in 88,8 % of 36 samples analysed with levels ranging from 5 to 256 eggs per 100 g^-1 of sediment. During the 3 campaigns, in November 1987 (first campaign) was obtained the smallest number of positive samples (9/12) and in March 1988 (second campaign) the highest number of positive samples seize all these samples contained helminth eggs. These eggs were of the Nematode and/or the Cestode class. All the positive samples (32/36) contained Nematode eggs whereas Cestode eggs are found only in 16 samples. The Nematode eggs were Ascaris, Toxacara and Trichuris, Capillaria; Cestode eggs Hymenolepis and Taenia. All the samples with Nematode eggs contained in decreasing amounts Toxocara (66,6 %), Ascaris (61 %) and Trichuris, Capliaria (22,2 %). Cestodes were predominantly Taenia (38,8 %), Hymenolepis (16,6%). The difference in behaviour between Nematode and Cestode eggs, the latter being much less frequent, was probably due to the greater fragility of Cestodes in a marine environment. The viability of the Ascaris eggs found on samples at the Besos area was 100 %. The samples from the effluent zone contained Ascaris eggs with viability ranging from 0 to 100 %. In the Barcelonetta area, 5 to 42 % of Ascaris eggs were viable.

These results obtained front seawater emphasize the necessity of further investigation into the extent of parasitological pollution on the marine environment by offshore flowing of treatment plant sludge, paying particular attention to the viability and the infection potential of the helminth eggs.

Keywords:

• Wastewater,
• sludge,
• helminth eggs,
• Nematodes,
• Cestodes,
• marine sediments,
• viability,
• Ascaris