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Cow dung for Bioremediation

Accord­ing to World Bank data, the amount of sol­id waste gen­er­at­ed by the world in a year is about 2 bil­lion tonnes. It is esti­mat­ed that at least 33 per­cent of this is not man­aged in an envi­ron­men­tal­ly safe man­ner [1]. Among the tox­ic pol­lu­tants are agri­cul­tur­al pes­ti­cides, phar­ma­ceu­ti­cals and byprod­ucts from petro­chem­i­cal indus­tries.

Pes­ti­cides

Ever since the indus­tri­al­iza­tion of agri­cul­ture, pes­ti­cide use has become wide­spread. Pes­ti­cides are chem­i­cal sub­stances or mix­tures of sub­stances that pro­tect crops and plants from pests, weeds and dis­eases. Humans and oth­er liv­ing organ­isms are exposed to pes­ti­cides through con­tact with the skin, inhala­tion and oral inges­tion. Sev­er­al research stud­ies show that these chem­i­cals are bio-accu­mu­lat­ed in the body. Bio-accu­mu­la­tion refers to the uptake of sub­stances from the envi­ron­ment by an organ­ism and its accu­mu­la­tion or reten­tion in the body over time. Adverse health effects such as dis­eases relat­ed to the skin, gas­troin­testi­nal tract, ner­vous sys­tem, res­pi­ra­to­ry, endocrine and repro­duc­tive sys­tems and can­cer have been linked with expo­sure to pes­ti­cides. High lev­els of expo­sure can even result in death. Although the con­cen­tra­tion of pes­ti­cides found in food such as fruits, veg­eta­bles and cere­als is with­in the leg­isla­tive “safe lim­its”, the com­bined expo­sure to two or more dif­fer­ent chem­i­cal sub­stances may have syn­er­gis­tic effects that could pose seri­ous health risks [2].

Phar­ma­ceu­ti­cals

Sim­i­lar to pes­ti­cides, phar­ma­ceu­ti­cal residues from the med­ical sec­tor are also present in the envi­ron­ment. Sev­er­al ana­lyt­i­cal stud­ies have shown the wide­spread occur­rence of these chem­i­cal com­pounds in soil and water sam­ples. Puck­ows­ki et al. did a rig­or­ous review of ana­lyt­i­cal stud­ies on phar­ma­ceu­ti­cals in the envi­ron­ment, such as antibi­otics, anti-hyper­ten­sives, anti­de­pres­sants, anal­gesics, anti-inflam­ma­to­ry drugs and steroids[3]

Phar­ma­ceu­ti­cals are inher­ent­ly bioac­tive com­pounds. Though they are present in the envi­ron­ment at low con­cen­tra­tions, their con­tin­u­ous input into the envi­ron­ment could lead to pro­longed expo­sure, there­by caus­ing adverse effects on non-tar­get organ­isms. Fur­ther­more, the rate at which these phar­ma­ceu­ti­cals are intro­duced into the envi­ron­ment exceeds their degra­da­tion rate, mak­ing them a per­sis­tent tox­ic con­t­a­m­i­nant in the envi­ron­ment [3].

Just like pes­ti­cides, these phar­ma­ceu­ti­cals also tend to bio-accu­mu­late in the body of organ­isms. While avail­able research stud­ies refer only to select­ed com­pounds, in real­i­ty, organ­isms are exposed to hun­dreds of phar­ma­ceu­ti­cal com­pounds simul­ta­ne­ous­ly. The health risks due to such syn­er­gis­tic effects have not been inves­ti­gat­ed.

Tox­in expo­sure and neu­rode­gen­er­a­tive dis­eases

Wide­spread expo­sure to tox­ic chem­i­cals and their bio-accu­mu­la­tion have been con­firmed as a cause of cog­ni­tive dys­func­tion and dementia[4]. The Cen­ter for Dis­ease Con­trol and Pre­ven­tion, USA, has found that most peo­ple have accu­mu­lat­ed an assort­ment of tox­ic chem­i­cals in their body, such as heavy met­als, pes­ti­cides and flame retar­dants. It is well-estab­lished that many of these chem­i­cals are neu­ro­tox­ins; they have a neu­rode­gen­er­a­tive as well as neu­rode­vel­op­men­tal impact as they lead to patho­log­i­cal mech­a­nisms such as dis­rup­tion of neu­ro­trans­mit­ter regulation[4].

The most com­mon type of demen­tia, Alzheimer’s dis­ease, is now grow­ing at an epi­dem­ic pace, with a huge bur­den of health­care costs that could dev­as­tate the world’s economies, health care sys­tems and fam­i­lies [4].

Biore­me­di­a­tion

For­tu­nate­ly, tox­i­cant expo­sure is reversible and it is pos­si­ble to detox­i­fy the envi­ron­ment of these chem­i­cals. This method is called biore­me­di­a­tion, defined as the use of nat­u­ral­ly occur­ring microbes such as bac­te­ria and fun­gi or genet­i­cal­ly engi­neered micro-organ­isms to detox­i­fy man-made pol­lu­tants. Earth­worms, for instance, have the capac­i­ty to detox­i­fy sev­er­al pes­ti­cides due to their intesti­nal microflo­ra.


Prin­ci­ple of Biore­me­di­a­tion

(Image cour­tesy: www.earthreminders.com)

One of the recent advances in biore­me­di­a­tion tech­nol­o­gy is the use of cow dung micro­bial con­sor­tia for detox­i­fi­ca­tion of pol­lu­tants. A micro­bial con­sor­tium refers to two or more bac­te­r­i­al groups liv­ing in a sym­bi­ot­ic rela­tion­ship (a close, mutu­al­ly ben­e­fi­cial bio­log­i­cal rela­tion­ship between two dif­fer­ent organ­isms).


Micro­bial con­sor­tium: Two or more bac­te­r­i­al groups liv­ing in a close, mutu­al­ly ben­e­fi­cial rela­tion­ship.

Cow dung for biore­me­di­a­tion

In the Indi­an tra­di­tion, cow dung is con­sid­ered a high­ly puri­fy­ing sub­stance. It is used to plas­ter the walls and floor of tra­di­tion­al homes, owing to its activ­i­ty against dis­ease caus­ing pathogens and sev­er­al oth­er prop­er­ties ben­e­fi­cial to human health. Even today, it is a com­mon sight to observe women sprin­kle cow dung mixed with water over the por­ti­co of the house ear­ly in the morn­ing. In the his­tor­i­cal epic, the Mahab­hara­ta, the great sage Vasish­ta describes the glo­ries of cows and explains how the cows prac­tised aus­tere penances for a hun­dred thou­sand years with the goal of attain­ing to a posi­tion of great emi­nence and becom­ing the res­cuers of the worlds.

“By bathing in water mixed with our dung, peo­ple shall become sanc­ti­fied. The deities and men shall use our dung for the pur­pose of puri­fy­ing all crea­tures mobile and immo­bile.”

Such is the boon grant­ed by Lord Brah­ma, the cre­ator of the uni­verse, to the cows [5]

Today. sci­en­tif­ic evi­dence shows that the micro­bial com­mu­ni­ties present in cow dung pos­sess remark­able poten­tial for biore­me­di­a­tion of pes­ti­cides, phar­ma­ceu­ti­cals and oth­er pol­lu­tants. Let us look at the find­ings of a few stud­ies.

Geetha et al. inves­ti­gat­ed the biore­me­di­a­tion of com­mon­ly used pes­ti­cides such as chlor­pyri­fos, fen­valer­ate, cyper­me­thrin, butoxyethyl ester at dif­fer­ent con­cen­tra­tions using cow dung micro­bial consortia.The process of biore­me­di­a­tion of the pes­ti­cide mixed soil was stud­ied till the par­ent com­pound was con­vert­ed into less harm­ful com­pounds, which even­tu­al­ly become a part of the micro­bial food chain and get inte­grat­ed with humic sub­stances (organ­ic mat­ter) in soil [6].

Mech­a­nisms for biore­me­di­a­tion: The cow dung was char­ac­ter­ized for physi­co-chem­i­cal and micro­bial para­me­ters. Two key fac­tors were found to be the rea­son for cow dung’s poten­tial in biore­me­di­a­tion:

  1. The cow dung slur­ry con­tained a robust, large, diverse pop­u­la­tion of microor­gan­isms such as bac­te­ria, fun­gi and actin­o­mycetes, which were effec­tive in the biodegra­da­tion of pes­ti­cide amend­ed soil.

  2. The high con­cen­tra­tion of nutri­ents in cow dung such as organ­ic car­bon, nitro­gen, phos­pho­rus, sul­phate, cal­ci­um chlo­ride, sodi­um, potas­si­um and mag­ne­sium pro­vide micro- and macro- nutri­tion for the micro­bial com­mu­ni­ty to grow and pro­lif­er­ate [7].

In oth­er words, the large micro­bial pop­u­la­tion and high­er nutri­ent avail­abil­i­ty was found to have a sig­nif­i­cant influ­ence on the biore­me­di­a­tion of pes­ti­cides.

Adap­ta­tion respons­es of bac­te­ria: Research on micro­bial mech­a­nisms of biore­me­di­a­tion of tox­ic com­pounds reveals that suc­cess­ful decon­t­a­m­i­na­tion requires bac­te­r­i­al strains that have the appro­pri­ate enzymes and the abil­i­ty to degrade par­tic­u­lar tox­ins. This abil­i­ty to degrade tox­ins pri­mar­i­ly depends on the adap­ta­tion mech­a­nisms that allow bac­te­ria to elim­i­nate tox­ic com­pounds in their envi­ron­ment and sur­vive. Many adap­ta­tion respons­es have been observed in bac­te­ria that coun­ter­act the effects of tox­ic pol­lu­tants in the envi­ron­ment. Exam­ples include sat­u­ra­tion-rigid­i­fi­ca­tion of the cell mem­brane, increased con­tent of spe­cif­ic fat­ty acids, pro­duc­tion of stress pro­teins and so on. Since the cell mem­brane is the first point of con­tact between the tox­in and the bac­te­r­i­al cell, most adap­tive mech­a­nisms are to do with the main­te­nance of the cell mem­brane flu­id­i­ty. As a result of these adap­tive process­es, the tox­ic com­pounds in their envi­ron­ment are elim­i­nat­ed or their neg­a­tive effects min­i­mized [8].

Rand­hawa et al did a review of research papers on biore­me­di­a­tion of bio­med­ical wastes, heavy met­als, arsenic, petro­le­um, ben­zene and phe­nol with cow dung [9]. Some of the key find­ings are dis­cussed below.

The man­age­ment of bio­med­ical wastes pos­es a chal­lenge because they pol­lute the soil, water and air, if incin­er­at­ed (as incin­er­a­tors pro­duce tox­ic gas­es like diox­ins). In one research study, it was found that a cer­tain species of fun­gus known as Peri­coniel­la present in cow dung, was an excel­lent degrad­er of bio­med­ical waste such as con­t­a­m­i­nat­ed ban­dages and cot­ton.

Anoth­er study found that Pseudomonas plecoglos­si­ci­da, iso­lat­ed from cow dung, was effec­tive in the biore­me­di­a­tion of insec­ti­cides like cyper­me­thrin (a fast-act­ing neu­ro­tox­in for insects). Sim­i­lar­ly, Pseudomonas aerug­i­nosa could be used in the biore­me­di­a­tion of chlor­pyri­fos, anoth­er pes­ti­cide that is a neu­ro­tox­in.

Such stud­ies high­light the poten­tial for these bac­te­r­i­al iso­lates from cow dung to be applied in the biore­me­di­a­tion of pes­ti­cide con­t­a­m­i­nat­ed soil and water. The microbes in cow dung also have the abil­i­ty to reduce arsenic con­cen­tra­tion in water.

Petro­le­um refiner­ies and petro­chem­i­cal indus­tries release com­plex organ­ic wastes such as ben­zene, phe­nol, toluene, naph­tha­lene, paraf­fin, etc. Pseudomonas and Bacil­lus species of bac­te­ria present in cow dung were iden­ti­fied as petro­le­um uti­liz­ing bac­te­ria that could degrade petro­le­um. Pseudomonas puti­da was found to be a poten­tial ben­zene and phe­nol degrad­er.

In sum­ma­ry, biore­me­di­a­tion using nat­u­ral­ly occur­ring microbes in cow dung is a pow­er­ful, low-cost approach to detox­i­fy the envi­ron­ment of per­sis­tent and bioac­cu­mu­la­tive chem­i­cal residues. It is a resource that is abun­dant­ly avail­able in rur­al areas of India. Fur­ther research and tech­nol­o­gy devel­op­ment in this area could go a long way in reclaim­ing our envi­ron­ment and our health for a sus­tain­able future.

REFERENCES

[1] Trends in Sol­id Waste Man­age­ment n.d. https://datatopics.worldbank.org/what-a-waste/trends_in_solid_waste_management.html (accessed March 28, 2021).

[2] Nicolopoulou-Sta­mati P, Maipas S, Kotam­pasi C, Stama­tis P, Hens L. Chem­i­cal Pes­ti­cides and Human Health: The Urgent Need for a New Con­cept in Agri­cul­ture. Front Pub­lic Heal 2016;4:148. https://doi.org/10.3389/fpubh.2016.00148.

[3] Puck­ows­ki A, Mio­duszews­ka K, Łukaszewicz P, Borec­ka M, Caban M, Maszkows­ka J, et al. Bioac­cu­mu­la­tion and ana­lyt­ics of phar­ma­ceu­ti­cal residues in the envi­ron­ment: A review. J Pharm Bio­med Anal 2016;127:232–55. https://doi.org/10.1016/j.jpba.2016.02.049.

[4] Genuis SJ, Kelln KL. Tox­i­cant expo­sure and bioac­cu­mu­la­tion: a com­mon and poten­tial­ly reversible cause of cog­ni­tive dys­func­tion and demen­tia. Behav Neu­rol 2015;2015:620143. https://doi.org/10.1155/2015/620143.

[5] The Mahab­hara­ta, Book 13: Anusasana Par­va: Sec­tion LXXIX n.d. https://www.sacred-texts.com/hin/m13/m13b044.htm .

[6] Geetha M, Fulekar M. Biore­me­di­a­tion of pes­ti­cides in sur­face soil treat­ment unit using micro­bial con­sor­tia. African J Env­i­ron Sci Tech­nol 2008;2:36–45.

[7] Fulekar MH. Biore­me­di­a­tion tech­nol­o­gy: recent advances 2012.

[8] Dony­i­nah SK. Per­sis­tent Organ­ic Pol­lu­tants. BoD–Books on Demand; 2019.

[9] Rand­hawa GK, Kullar JS. Biore­me­di­a­tion of phar­ma­ceu­ti­cals, pes­ti­cides, and petro­chem­i­cals with gomeya/cow dung. ISRN Phar­ma­col 2011;2011:362459. https://doi.org/10.5402/2011/362459.

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