Fertilización con Purines y Estiércol de Cerdo: Repercusiones sobre la Salud Pública

La fertilización con estiércoles y purines de granjas industriales con vistas a la crianza de animales comestibles acarrea riesgos para la salud humana, dado la cantidad de patógenos que pueden albergar. En consecuencia, se requieren planificaciones y una gestión adecuada de estos productos a cargo de las administraciones públicas. La noticia que trataremos brevemente hoy muestra que “en un caso concreto” cuando tales reglamentos son apropiados y cumplidos, se pueden evitar, en gran medida, los riesgos de contraer enfermedades infecciosas, salvaguardando la salud pública ciudadana. En cualquier caso deben tenerse en cuenta los patógenos que albergan tales sustancias fertilizantes, ya que son variados y considerables. Estos datos dan fe del problema inherente que acarrean tales tipos de fertilizaciones en los suelos de cultivo. Reiteramos que en el caso mentado de EE.UU., tanto la legislación como su cumplimiento fue efectiva, ya que aunque se detectaron más microorganismos patógenos en las parcelas tratadas con estiércoles y/o purines de cerdo (francamente no me queda claro), estos no parecieron significar un problema sanitario. En algunos casos concretos, como el de la listeria (que si produce infecciones en humanos, al contrario de lo que se deduce de una lectura del enlace) se presentaba en los campos no tratados, ya que pueden portados por animales silvestres previamente infectados.

Rociando con Purines o estiercol de Cerdo. Fuente: Crops Science Society of America

De cualquier modo, la lista de patógenos testados encontrados es más que preocupante a pesar de que sus concentraciones fueran bajas. El nombre de los variados géneros que a continuación aparecen en las dos noticias que incluimos abajo, así como en la publicación adicional, debe convencernos de que no se debe bajar la guardia. Y por una vez más debemos recalcar que se trata de resultados de áreas sometidas a una legislación adecuada y no de otros muchos casos en que esta no existe o es incumplida por los granjeros de animales comestibles (en este caso el cerdo) y/o por los propios agricultores. Digamos de paso que los problemas se agravan sobre manera si se riega con aguas residuales no tratadas adecuadamente. Notar que también se comprobaron los efectos sobre distintos tipos de suelos, aspecto que raramente suele acaecer en países como España, entre otros. También es cierto que este estudio no nos informa acerca de los virus. Ese puede ser otro asunto.

Rotura de Embalses con residuos de cerdo tras inundación. Fuente: Photo Rick Dove, Neuse Riverkeeper. Fuente Environmental Reserach Perspective

Finalmente comentar que el emplazamiento de las balsas en donde se almacenan estos residuos agroindustriales debe ser escogida con sumo cuidado, no se que su rotura, por una u otra causa (mala construcción, deterioro, inundaciones, seísmos, u otros desastres naturales), genera el vertido de los mismos en las aguas corrientes generando gravísimos problemas ambientales y de salud, como se constata en el enlace que se ofrece junto a la foto de abajo.

Juan José Ibáñez

Southern Soils Mitigate Manure Microbes

ScienceDaily (Sep. 9, 2010) — That swine manure sprayed on to fields adds valuable nutrients to the soil is well known. But what is not known is whether all that manure is bringing harmful bacteria with it.

A new study looks at the levels of nutrients and bacteria in soils of fields that have been sprayed with manure for fifteen years or more. The research team, composed of scientists from the USDA-ARS Crop Science Research Laboratory at Mississippi State, tested soils inside and outside fields of five farms on twenty different soils types. Their results are reported in the September-October 2010 Journal of Environmental Quality, published by the American Society of Agronomy, the Crop Science Society of America, and the Soil Science Society of America.

Manure sprayed fields were found to contain higher concentrations of several types of bacteria. These include measurements of total bacteria, fecal bacteria, Staphylococcus (a common bacteria living inside animals and a potential human pathogen) and Clostridium (common gut inhabitants and potential pathogens).

Two other types of bacteria that are potential pathogens, E.Coli and Enterococcus, showed no differences in between sprayed or non-sprayed fields. One type of bacteria, Listeria, was found in higher concentrations outside, rather than inside, the fields. Two gastrointestinal pathogens, Campylobacter and Salmonella, could not be cultured in any significant amount from the fields, although DNA testing did detect some bacteria, though there were no differences between sprayed and non-sprayed fields.

The investigators also analyzed public health data from three public health districts with similar land areas, populations, and agricultural bases, but with varying numbers of swine confined animal feeding operations (CAFOs), a typical source of swine manure. Their analysis of annual reports of illnesses caused by Campylobacter and Salmonella from 1993 through 2008 showed no relationship between reported cases of these human illnesses and swine CAFO numbers.

The research team also tested soils for nutrient levels. These tests showed higher pH and higher levels of phosphorus, potassium, magnesium, sodium, copper, and zinc inside spray fields compared to outside. These results were consistent with what was expected for spray fields after long-term use. Finding differences between the same soil types inside and outside confirmed that outside soils had not been contaminated with manure and would provide good comparisons of bacteria.

«Finding low levels of pathogens outside spray fields is not surprising, because these bacteria are known to infect a wide range of wild and domestic birds and animals,» said team leader Mike McLaughlin.

Team microbiologist, John Brooks, added, «Finding similar low levels inside and outside the spray fields suggests that the low levels of pathogens in [manure] are further diluted in spray fields and either do not survive in soil or survive at low levels below cultural detection limits.»

This first report on spray field bacteria in the region suggests that manure nutrient management plans have been effective for nutrients and for bacterial pathogens. Future research will focus on enhanced resolution of pathogen levels in manure and soils, on pathogen survival and transport in soil and on plants, and on practical solutions to further reduce or eliminate risks from these pathogens.

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Story Source: The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by American Society of Agronomy.

Journal Reference: Michael R. McLaughlin, John P. Brooks, Ardeshir Adeli, John J. Read. Comparison of Selected Nutrients and Bacteria from Common Contiguous Soils Inside and Outside Swine Lagoon Effluent Spray Fields after Long-Term Use. Journal of Environment Quality, 2010; 39 (5): 1829 DOI: 10.2134/jeq2009.0447

Research Project: SAFE MANAGEMENT AND UTILIZATION OF WASTE FROM ANIMAL PRODUCTION

Location: Genetics and Precision Agriculture Research

Title: Comparison of selected nutrients and bacteria from common contiguous soils inside and outside swine lagoon effluent spray fields after long-term use

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 18, 2010
Publication Date: August 1, 2010
Reprint URL: http://doi:10.2134/jeq2009.0447

Citation: McLaughlin, M.R., Brooks, J.P., Adeli, A., Read, J.J. 2010. Comparison of selected nutrients and bacteria from common contiguous soils inside and outside swine lagoon effluent spray fields after long-term use. Journal of Environmental Quality. 39:1829-1840.

Interpretive Summary: This study documented the amounts of selected nutrients, fecal bacteria and bacterial pathogens in soils after more than 15 years of swine lagoon effluent applications. This is the first report to document levels of fecal and pathogenic bacteria in soils of long-term spray fields in the Mid-South region of the US. The findings suggest that swine manure management plans in the region have been effective and appropriate. Levels of the bacterial pathogens Campylobacter spp., Listeria spp. and Salmonella spp. found in spray field soils were relatively low and did not differ from background levels found outside the spray fields. In fact, Campylobacter spp. and Salmonella spp. could not be cultured from any soil samples, although molecular tests confirmed the presence of DNA for both, indicating that both were or had been present, as was expected based on an earlier and separate study of lagoon effluents. We conclude from the present and earlier work that the bacterial pathogen load transported to spray field soils during the 2008 irrigation season was relatively low, declined by natural die off during the winter and reached background levels before the 2009 irrigation season. Results of the present study showed no evidence of cumulative buildup of bacterial pathogens in spray field soils. Risk assessment models for bacterial pathogen contamination from land application of swine lagoon effluents have not been developed, and although low pathogen levels found in the present study are encouraging, more research on temporal distribution of pathogens and new models are needed to fully assess potential risks.

Technical Abstract: Swine (Sus scrofa domestica) lagoon effluent is a valuable fertilizer. In the Mid-South US it is applied to grass hay in spray-irrigated fields from April to September. Lagoon levels of nutrients and bacteria, and soil levels of nutrients, were known, but little was known of effluent bacterial levels in soil. The present study determined and compared the presence and levels of effluent bacteria, including human pathogens, and nutrients in soils inside and outside spray fields after >15 yr of effluent fertilization. Four soils were sampled at each of five locations in February and March 2009. Cores (0 to 5 cm and 5 to 10 cm deep) were tested for bacteria. Adjacent (<10 cm) cores (0 to15 cm deep) were tested for nutrients. Five cores collected at 15 m intervals were combined to comprise each sample. Analyses showed higher pH and Mehlich-3-extracable (M3-) P, Mg, K, Na, Cu and Zn inside than outside spray fields, while total N, total C, M3-Ca and M3-Mn did not differ. Levels for heterotrophic plate counts, thermotolerant coliforms, Staphylococcus spp. and Clostridium perfringens (Veillon and Zuber) Hauduroy et al. were higher inside than outside spray fields, but Escherichia coli (Migula) Castellani and Chalmers and Enterococcus spp. were not. Cultural presence/absence tests for Listeria spp., Campylobacter spp. and Salmonella spp. detected only Listeria spp. (23% of samples inside and 28% outside), while molecular tests detected all three at low levels that were not different inside and outside spray fields. The pathogens occur naturally outside the spray field, while those from effluent do not survive or survive at low levels inside spray fields.