2017-05-25 13:12:08
Algal bloom and fish death. 
Source: Internet
Recent fish and bird deaths from flash flooding in northeast Bangladesh are probably due to blue-green algae that flourished in the waters. Much fertilization with urea and phosphates had been done on rice paddies prior to the floods. These are rich sources of available nitrogen and phosphorus nutrients that the blue-green algae (also called cyanobacteria) love. Once the floodwaters mobilized the fertilizer, the cyanobacteria were in ideal conditions to multiply. Their rapid growth leads to conditions that can easily cause massive die-offs of animals such as have been widely reported elsewhere in the world.
Cyanobacteria have been implicated for deaths in fish, bird, livestock and even human populations. Events in which algae reproduce dramatically are called “blooms”. Water samples from Dekhar haor and Khacher haor showed phosphorus levels that were two to three times higher than normal, 0.07 and 0.09 mg/L respectively as opposed to less than 0.03 normally. At Tangua haor, where few wildlife deaths were found, the phosphorus level was lower at 0.05 mg/L.
Cyanobacteria release poisons known as cyanotoxins. Some of these are among the most powerfully toxic substances known. Cyanobacteria can produce neurotoxins (affecting the nervous system), hepatotoxins (damaging the liver), cytotoxins (affecting cell metabolism) and endotoxins (triggering allergic immune responses). The specific toxins depend on which particular species of cyanobacteria are present. To completely understand these animal deaths, it will be necessary to determine which blue-green algae contributed to these blooms.
Preliminary examination of water samples from the area had visible suspensions of blue-green algae although their specific types are not yet known.
Preliminary microbial analysis of samples was performed in the department of microbiology under the supervision of Dr Anowar Khasru Parvej, Professor of Microbiology and water quality tests were performed by Dr. Baki Billah of the department of zoology at the Jahangirnagar University. Microscopic techniques reveal evidence of an algal bloom in at least two of the Hoars samples. This was further supported by the most probable number (MPN) technique, a method familiar to quality control (QC) microbiologists as part of the microbial limits tests, which showed an uncountable number of microorganisms along with the presence of deadly pathogens including cyanobacteria. Dr. Maqsud Hossain, director of the newly established “North South University Genome Research Institute” (NGRI) is in the process of characterizing isolates using molecular techniques and will conduct whole genome sequencing of any isolated pathogens. They also plan to perform meta-genomics analysis to find the presence of any other pathogens in the samples using their state-of-the-art, high throughput genome sequencing facilities.
Fish living in the algal blooms had a double dose of trouble. Not only were they possibly subject to cyanotoxins, but they were also in waters that were depleted in dissolved oxygen for them to breath. The algal blooms create much organic material that must be decomposed, both metabolic wastes and dead cells. As they decompose they consume the dissolved oxygen that the fish need. Water samples from Dekhar haor and Khacher haor showed biochemical oxygen demands (BOD, a measure of how much organic material could be decomposed) that were five to six times higher than normal, 12.77 and 13.56 mg/L versus a normal 2.5 mg/L. These same two locations had dissolved oxygen levels that were less than a quarter of normal values, 1.5 and 1.2 mg/L versus a normal 5 mg/L. At Tangua haor, where fewer wildlife deaths were reported, the BOD level was slightly elevated at 3.12 mg/L and the dissolved oxygen content was a normal 5.4 mg/L.
A good understanding of what caused this event and how to prevent it in the future will require some field studies. Dr Mohammad A. Kadir who is called about the problem and investigating the problem locally will also supervise the sample collection. Spectating the blue-green algae that are naturally found in the area, the normal water quality needs to be characterized. Regular sampling of waters in the troubled areas should confirm the algal bloom diagnosis plus provide a baseline for what health conditions are. There may be methods of fertilizing rice paddies that do not leave the area vulnerable to future algal blooms.
There is speculation that the fish and bird deaths were due to uranium contamination from upstream mines. This does not seem likely from the standpoint of the exposures that would be necessary to cause such rapid deaths. Additionally, if radiation exposures were lethal, the dead animals should show external radiation burns and lesions. The dilution that any dissolved or suspended radioactive materials have undergone in being transported to the die-off sites makes this cause seem remote. Radioactive monitors by investigating teams would have been “screaming” if this explanation is correct. It would have been dangerous for field personnel to even be there still. Radiation deaths are usually spread out over time, not massive instantaneous die-offs. Many deaths from radiation exposure come from subsequent infections that invade skin lesions or burned areas.
The pHs noted in the samples are also not consistent with poisoning from acid mine drainage, aluminium, dissolved heavy metals or ammonia.
The whole work was jointly carried out by Dr Md. Mainul Hossain and Dr Ayesha Sharmin. Dr Md Mainul Hossain chemistry as Assistant Professor in the Biochemistry and Microbiology Department, North South University and obtained a PhD in Analytical/Environmental Chemistry from University of Montana, Missoula, USA. Dr Aysha Sharmin is also a chemist and Assistant Professor in the chemistry department of Bangladesh University Engineering and Technology (BUET).Dr. Ayesha Sharmin Dr Garon C. Smith, an analytical/environmental chemist with broad interests in air and water characterization, did supervise the work. He teaches freshman chemistry and undergraduate and graduate courses in analytical and environmental chemistry in the Unversity of Montana, the USA as a Professor.
Such death of fish and birds in the aquatic habitats due to algal bloom are frequently reported from around the world. Searching google with the keywords ” Algal bloom” shows many such reports.
Bangladesh should have developed mechanisms and aware people so that recurrence of the event can be prevented and damage restricted.
