Биологические науки/7. Зоология

Sinturina A.V.

Kazakh national university named after al-Farabi, Kazakhstan

Changes of trophic activity of EISENIA FETIDA under influence of heavy metals ions

Earthworms are of a great import in forming of quality and fertility of soil due to their trophic activity. As they have a high quantity in most of biocenoses and ability to reach deep levels of soil and to move large amounts of earth during their life, earthworms play an important role in processes of biogenic migration of chemical elements. Earthworms are able to reduce technogenic soil pressure by accumulation of some heavy metals as well.

As a whole, rate of mechanical destruction of plant residues and quality of its transformation in earthworms intestines depends as on properties of organic material as on characteristics of animal organism. Digestive tract shows most structural reorganization at changing of feeding type of different earthworms ecological groups. It also shows most contact with peroral incoming toxicants from soil and plant residues [1, 2]. Hence it is important to know influence of environmental conditions changing, different toxicants etc. on functional state of this system of invertebrate organism.

The aim of our experiment was investigation of influence of heavy metals high concentration on trophic activity of earthworms, to be exact on rate of food passing through intestines and on average mass of dietary intake. As an object of investigation was taken widespread species, Eisenia fetida. This species enters into processing of organic residues on early stages of destruction, it is also characterized by large volume of daily dietary ration per mass and high prolificacy (up to 5 cocoons per 10 days from 1 earthworms) in comparison with other species of the same ecological group. Eisenia fetida is also of a high tolerance to considerable variation of abiotic factors (temperature 0-27⁰C, soil moisture 3-98%, pH 7-7,6), and in case of maximal and minimal value of these parameters Eisenia fetida doesn’t diapause and continues to feed. Due to these properties Eisenia fetida is one of the most explotable species in agriculture [3].

Only mature individuals of Eisenia fetida, with well-defined clitellum were taken for experiment. Contaminated with heavy metals soil was taken from the territory of concentrating department of metallurgical works in Temirtau city. Control soil (with low content of heavy metals) was taken in park zone of Abai city. Determination of heavy metals concentration (Pb, Zn, Cd) in soil and in earthworms bodies was done by atomic absorption method.

Concentration of heavy metals in earthworms bodies was determined before the beginning of the experiment. We used Striganiva’s method for determination of rate of food passing through intestines and of average mass of dietary intake [4]. Select group of individuals were placed into containers with the control soil to get the group with minimal amount of heavy metals. After cocoon production parental individuals were removed, while cocoons were stayed in containers. Concentration of heavy metals was determined in hatched mature earthworms and compared with parental.

Propagative earthworms were placed by 20 into containers filled with contaminated soil and into one container with control soil. The volume of each container is 300 cm³. The experiment was done in five-fold repeatability. During the experiment optimal conditions were maintained (temperature 20-25⁰, soil moisture – 65-75%).

Content of heavy metals in Eisenia fetida individuals taken from Bukpa river was a little bit less then maximum permissible concentration. These data correlated with amount of metals in the soil of the river bank. When progeny on the uncontaminated substrate was gained, concentration of metals in it was significantly less then maximum permissible concentration. Content of heavy metals in the soil from the territory of concentrating department of metallurgical works of Temirtau city significantly exceeds maximum permissible concentration.

Trophic activity data of the earthworms in control samples remained stable during all the period of the experiment: rate of food passing through intestines was 4,1±0,01 h, average mass of dietary intake was 164,58±0,01 mg/g of live weight, live weight of earthworms was 0,387±0,01 g.

Earthworms placed into contaminated soil didn’t feed for the first two days, however live weight of the worms descended insignificantly. On the third day worms began to feed and their mass of dietary intake was three times less than normal. For the next 5 days this parameter remained at the same level, while live weight gradually increased, but didn’t reach normal weight. Then gradual growth of dietary intake mass begins and achieves normal level at 23^rd day as well as live weight.

Rate of food passing through intestines significantly slowed after introduction of worms into the contaminated soil and the gradually comes to normal state. Thus this parameter restores faster than mass of dietary intake (fig.1).

Figure 1 Dynamics of earthworms basic trophic parameters restoration under influence of heavy metals

So organism of Eisenia fetida responds to the influence of large concentrations of heavy metals by slowing down of rate of food passing through intestines and significant decreasing of average mass of dietary intake; complete termination of feeding appears only for the first two days. Probably by this manner Eisenia fetida limits intake of heavy metals for the first time through the digestive system, admitting it through the cutaneous covering. This response is probably and adaptative mechanism, that is regulated by immune system. As it is shown on figure 4, rate of food passing through the intestines restores first, then live weight and the mass of dietary intake is last.

Rate of food passing through intestines is controlled by intestines smooth muscles activity, and average mass of dietary intake depends as on digestive enzymes activity as on system of neutralization and excretion of heavy metals. As restoration of rate of food passing occurs more rapidly then restoration of dietary intake we can suggest that nervous system recovers more rapidly than immune system.

Literature:

1. Striganova B.R., Pantosh-Derimova T.D., Tiunov A.V. Comparative evoluation of nitrogen fixation in interstines of different earthworms species. Proceedings of the Academy of Sciences Biological series? 1990 / - Vol. 2. p. 257-263 (in Russian)

2. Jordan D., Hubbard V.C., F. Ponder Jr., Berry E.C. The influence of soil compaction and removal of organic matter on two native earthworms and soil properties in an oak-hickory forest. Biology and fertility of soils. 2000. pp. 323-328

3. Novikova A.V. Features of vital functions of Eisenia fetida. Ecological issues of current importance. Materials of 3^rd international scientific and practical conference. 2-3 of december 1^st part. Karaganda. 2004. p. 182-183 (in Russian)

4. Striganova B.R. Determination of dietary intake of earthworms (Oligochaeta, Lumbricidae). Reports of the Academy of Sciences of USSR, 1982. - Vol. 2. – P. 266. (in Russian)