Argentina’s Default Clock Runs Out as Debt Talks Collapse.

http://www.bloomberg.com/news/2014-07-31/argentina-s-default-clock-runs-out-as-debt-talks-collapse.html

With Standard & Poor’s saying Argentina is in default and last-minute plans to remedy the situation falling through, investor focus is turning to whether holders of $29 billion of bonds will demand immediate repayment.

The nation missed a deadline yesterday to pay $539 million in interest after two full days of negotiations in New York failed to produce an accord with creditors from its last default in 2001. A U.S. judge ruled that the payment couldn’t be made unless those investors, a group of hedge funds led by Elliott Management Corp., got the $1.5 billion they claimed.

As Economy Minister Axel Kicillof returns to Buenos Aires with no set plans for further discussions with the hedge funds he described as “vultures,” other creditors must decide whether to invoke a clause that entitles them to demand their money back. While an 11th-hour attempt last night by a group of Argentine banks to avert a crisis by purchasing the securities from Elliott fell through, bondholders probably will give the parties more time to reach a settlement, according to Bank of America Corp.

“It’s in their best interest to delay acceleration and not introduce more difficulties,” Jane Brauer, a strategist at Bank of America, said by phone from New York. “The best thing for Argentina to do is to continue seeking a solution.”

Argentina has about $29 billion of bonds sold in international markets and denominated in foreign currencies with so-called cross-default provisions. Under their terms, Argentina would have to pay back the entire balance -- plus unpaid interest -- if at least 25 percent of holders demand that their money be returned. The potential liabilities are equal to the country’s foreign reserves, which are already hovering close to an eight-year low.

Previous Swaps

S&P’s declaration came after the expiration yesterday of a 30-day grace period on the original June 30 payment deadline. If Argentina is able to figure out a way to make its debt payments, the ratings could be revised “depending on our assessment at that time of Argentina’s residual litigation risk, its access to international debt markets and its overall credit profile,” S&P said.

RUFO Clause

He said Argentina couldn’t pay the $1.5 billion verdict to the hedge funds because doing so would require the country to similarly sweeten terms for investors who went along with the country’s debt restructurings in 2005 and 2010 and got 30 cents on the dollar. That stipulation, known as the RUFO clause, could trigger claims of more than $120 billion, the country has said.

Real Suffering

The economy, already headed for its first annual contraction since 2002 amid 40 percent inflation, will suffer in a default scenario as Argentines scrambling for dollars cause the peso to weaken and activity to slump, according to Hernan Yellati, the head of research at Banctrust & Co.

Step Backward

The country also changed its methodology for calculating inflation statistics after being faulted by the International Monetary Fund for flawed reporting.

Missing the debt payments represent a step backward in those efforts, according to Marco Santamaria, a New York-based money manager at AllianceBernstein, which oversees $25 billion of emerging-market debt. Argentina hasn’t issued global bonds since the default in 2001.

“A lot of the goodwill and positive signals that had come out of Buenos Aires are going to be diluted,” he said.

Traffic on Avenida 9 de Julio in downtown Buenos Aires, Argentina.

Pondweed.

http://en.wikipedia.org/wiki/Lotic_system_ecology

                                                      Pondweed is an autochthonous energy source.

Water Hyacinth.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Common water hyacinth in flower

Periphyton.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Periphyton are Algae which the most significant sources of primary production in most streams and rivers.

Example of decomposition of a leaf fallen into a Stream.

http://en.wikipedia.org/wiki/Lotic_system_ecology

 Allan gives the example of a leaf fallen into a stream. First, the soluble chemicals are dissolved and leached from the leaf upon its saturation with water. This adds to the DOM load in the system. Next, microbes such as bacteria and fungi colonize the leaf, softening it as the mycelium of the fungus grows into it. The composition of the microbial community is influenced by the species of tree from which the leaves are shed (Rubbo and Kiesecker 2004). This combination of bacteria, fungi, and leaf are a food source for shredding invertebrates,which leave only FPOM after consumption. These fine particles may be colonized by microbes again or serve as a food source for animals that consume FPOM. Organic matter can also enter the lotic system already in the FPOM stage by wind, surface runoff, bank erosion, or groundwater. Similarly, DOM can be introduced through canopy drip from rain or from surface flows.

Allochthonous energy Sources.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Allochthonous energy sources are those derived from outside the lotic system, that is, from the terrestrial environment. Leaves, twigs, fruits, etc. are typical forms of terrestrial CPOM that have entered the water by direct litterfall or lateral leaf blow.In addition, terrestrial animal-derived materials, such as feces or carcasses that have been added to the system are examples of allochthonous CPOM. The CPOM undergoes a specific process of degradation.

Decomposition of dead Organisms is also an Autochthonous energy Source.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Another form of autochthonous energy comes from the decomposition of dead organisms and feces that originate within the lotic system. In this case, bacteria decompose the detritus or coarse particulate organic material (CPOM; >1 mm pieces) into fine particulate organic matter (FPOM; <1 mm pieces) and then further into inorganic compounds that are required for photosynthesis.This process is discussed in more detail below.

Autochthonous energy Sources.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Autochthonous energy sources are those derived from within the lotic system. During photosynthesis, for example, primary producers form organic carbon compounds out of carbon dioxide and inorganic matter. The energy they produce is important for the community because it may be transferred to higher trophic levels via consumption. Additionally, high rates of primary production can introduce dissolved organic matter (DOM) to the waters.

(Trophic Relationships) Energy Inputs.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Energy sources can be Autochthonous or Allochthonous.

Other vertebrate taxa that inhabit lotic Systems Include:-

http://en.wikipedia.org/wiki/Lotic_system_ecology

 Other vertebrate taxa that inhabit lotic systems include amphibians, such as salamanders, reptiles (e.g. snakes, turtles, crocodiles and alligators) various bird species, and mammals (e.g., otters, beavers, hippos, and river dolphins). With the exception of a few species, these vertebrates are not tied to water as fishes are, and spend part of their time in terrestrial habitats.Many fish species are important as consumers and as prey species to the larger vertebrates mentioned above.

Lotic systems typically connect to each Other.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Lotic systems typically connect to each other, forming a path to the ocean (spring → stream → river → ocean), and many fishes have life cycles that require stages in both fresh and salt water. 
Salmon, for example, are anadromous species that are born and develop in freshwater and then move to the ocean as adults. 
Eels are catadromous, and are born and develop in the ocean and then move into freshwater as adults.

Fish and other Vertebrates.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Fishes are probably the best-known inhabitants of lotic systems. The ability of a fish species to live in flowing waters depends upon the speed at which it can swim and the duration that its speed can be maintained. This ability can vary greatly between species and is tied to the habitat in which it can survive. Continuous swimming expends a tremendous amount of energy and, therefore, fishes spend only short periods in full current. Instead, individuals remain close to the bottom or the banks, behind obstacles, and sheltered from the current, swimming in the current only to feed or change locations.Some species have adapted to living only on the system bottom, never venturing into the open water flow. These fishes are dorso-ventrallyflattened to reduce flow resistance and often have eyes on top of their heads to observe what is happening above them. Some also have sensory barrels positioned under the head to assist in the testing of substratum (Brown 1987).

(Biotic Factors in Rivers) Insects and other Invertebrates.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Up to 90% of invertebrates in some lotic systems are insects. These species exhibit tremendous diversity and can be found occupying almost every available habitat, including the surfaces of stones, deep below the substratum, adrift in the current, and in the surface film. Insects have developed several strategies for living in the diverse flows of lotic systems. Some avoid high current areas, inhabiting the substratum or the sheltered side of rocks. Additional invertebrate taxa common to flowing waters include mollusks such as snails, limpets, clams, mussels, as well as crustaceans like crayfish and crabs.Like most of the primary consumers, lotic invertebrates often rely heavily on the current to bring them food and oxygen (Brown 1987). Invertebrates, especially insects, are important as both consumers and prey items in lotic systems.

Living in flowing water can be beneficial to Plants.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Living in flowing water can be beneficial to plants and algae because the current is usually well aerated and it provides a continuous supply of nutrients.These organisms are limited by flow, light, water chemistry, substrate, and grazing pressure.Algae and plants are important to lotic systems as sources of energy, for forming microhabitats that shelter other fauna from predators and the current, and as a food resource (Brown 1987).

Plants exhibit limited adaptations to fast flowing Waters.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Plants exhibit limited adaptations to fast flow and are most successful in reduced currents. More primitive plants, such asmosses and liverworts attach themselves to solid objects. This typically occurs in colder headwaters where the mostly rocky substrate offers attachment sites. Some plants are free floating at the water’s surface in dense mats like duckweed or water hyacinth. Others are rooted and may be classified as submerged or emergent. Rooted plants usually occur in areas of slackened current where fine-grained soils are found (Brown 1987).These rooted plants are flexible, with elongated leaves that offer minimal resistance to current.

Primary Producers.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Algae, consisting of phytoplankton and periphyton, are the most significant sources of primary production in most streams and rivers.Phytoplankton float freely in the water column and thus are unable to maintain populations in fast flowing streams. They can, however, develop sizable populations in slow moving rivers and backwaters. Periphyton are typically filamentous and tufted algae that can attach themselves to objects to avoid being washed away by fast current. In places where flow rates are negligible or absent, periphyton may form a gelatinous, unanchored floating mat.

IPhone-Ready Apps Mean Teens Tracked Without Calling Home.

http://www.bloomberg.com/news/2014-07-30/iphone-ready-apps-mean-teens-tracked-without-calling-home.html

Becca Ludlum knows better than to expect her teen son, Michael, to call home as he skateboards from the mall to the park to friends’ homes on long summer days.

Ludlum instead relies on a downloadable smartphone application called Life360 that uses satellite signals to follow the kid’s comings and goings.

“If he’s late to dinner, I can check where he is,” said Ludlum, a 36-year-old blogger from Tucson,Arizona. “He is not going to call me every time he gets somewhere -- he gets embarrassed.”

As teens in growing numbers adopt smartphones with global positioning system technology, they’re easier to keep tabs on using mobile apps like Life360. This rising tide of tracker apps creates a host of new ways for families to stay connected and coordinate schedules even as it heightens concerns about young people’s privacy.

The percentage of 13- to 17-year-olds using mobile phones rose to 70 percent last year from 58 percent in 2012, according to Nielsen. A reflection of the rising number of kids on phones, Life360 Inc., Glympse Inc., TWT Digital Ltd.’s ZoeMob and other developers of location-monitoring software have seen downloads jump at least 50 percent this year. Apple Inc.’s iPhone also comes with a widely used location feature, called Find My Friends.

“Even small children are getting smartphones, and that, of course, expands the addressable market significantly,” Andre Malm, an analyst at Berg Insight AB, said of the market for location-based apps.

Introduced four years ago, Life360 is adding 2 million new users a month, and just passed 100 million members, up from 63 million at the end of 2013. ZoeMob has notched up 2.3 million downloads this year, for a total of 7.3 million. Glympse, based in Seattle, has experienced its fastest growth in the past four months since the app debuted in 2009, according to Chief Executive Officer Bryan Trussel.

Privacy, Carriers

Because family-tracking software keeps data on identities and exact locations, privacy controls are a key consideration for developers of the programs. Most apps let users turn their location-monitoring on and off, and require them to go through an extensive opt-in process.

The apps are also designed so that only a pre-defined group of users can access individual locations, rather than making tracking data publicly available.

Premium features also enable uses that go beyond finding out where family members are. Parents can receive alerts if a teen driver is exceeding speed limits, and users can get emergency help or contact a personal assistant.

Glympse, based in Seattle, has experienced its fastest growth in the past four months since the app debuted in 2009, according to Chief Executive Officer Bryan Trussel.

Introduced four years ago, Life360 is adding 2 million new users a month, and just passed 100 million users, up from 63 million at the end of last year.

Stream is a Lotic Ecosystem.

http://en.wikipedia.org/wiki/Lotic_system_ecology

This stream in the redwoods together with its environment can be thought of as forming a river or lotic ecosystem.

Biotic Factors.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Bacteria

Bacteria are present in large numbers in lotic waters. Free-living forms are associated with decomposing organic material, biofilm on the surfaces of rocks and vegetation, in between particles that compose the substrate, and suspended in the water column. Other forms are also associated with the guts of lotic organisms as parasites or in commensal relationships.Bacteria play a large role in energy recycling.

Substrate.

http://en.wikipedia.org/wiki/Lotic_system_ecology

The inorganic substrate of lotic systems is composed of the geologic material present in the catchment that is eroded, transported, sorted, and deposited by the current. Inorganic substrates are classified by size on the Wentworth scale, which ranges from boulders, to pebbles, to gravel, to sand, and to silt.Typically, particle size decreases downstream with larger boulders and stones in more mountainous areas and sandy bottoms in lowland rivers. This is because the higher gradients of mountain streams facilitate a faster flow, moving smaller substrate materials further downstream for deposition.Substrate can also be organic and may include fine particles, autumn shed leaves, submerged wood, moss, and more evolved plants.Substrate deposition is not necessarily a permanent event, as it can be subject to large modifications during flooding events.

Oxygen.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Oxygen is likely the most important chemical constituent of lotic systems, as all aerobic organisms require it for survival. It enters the water mostly via diffusion at the water-air interface. Oxygen’s solubility in water decreases as water pH and temperature increases. Fast, turbulent streams expose more of the water’s surface area to the air and tend to have low temperatures and thus more oxygen than slow, backwaters.Oxygen is a byproduct of photosynthesis, so systems with a high abundance of aquatic algae and plants may also have high concentrations of oxygen during the day. These levels can decrease significantly during the night when primary producers switch to respiration. Oxygen can be limiting if circulation between the surface and deeper layers is poor, if the activity of lotic animals is very high, or if there is a large amount of organic decay occurring.

Chemistry.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Water chemistry between systems varies tremendously. The chemistry is foremost determined by inputs from the geology of its watershed, or catchment area, but can also be influenced by precipitation and the addition of pollutants from human sources.Large differences in chemistry do not usually exist within small lotic systems due to a high rate of mixing.

 In larger river systems, however, the concentrations of most nutrients, dissolved salts, and pH decrease as distance increases from the river’s source.

Temperature.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Most lotic species are poikilotherms whose internal temperature varies with their environment, thus temperature is a key abiotic factor for them. Water can be heated or cooled through radiation at the surface and conduction to or from the air and surrounding substrate. Shallow streams are typically well mixed and maintain a relatively uniform temperature within an area. In deeper, slower moving water systems, however, a strong difference between the bottom and surface temperatures may develop. Spring fed systems have little variation as springs are typically from groundwater sources, which are often very close to ambient temperature. Many systems show strong diurnal fluctuations and seasonal variations are most extreme in arctic, desert and temperate systems.The amount of shading, climate and elevation can also influence the temperature of lotic systems.

Light.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Light is important to lotic systems, because it provides the energy necessary to drive primary production via photosynthesis, and can also provide refuge for prey species in shadows it casts. The amount of light that a system receives can be related to a combination of internal and external stream variables. The area surrounding a small stream, for example, might be shaded by surrounding forests or by valley walls. Larger river systems tend to be wide so the influence of external variables is minimized, and the sun reaches the surface. These rivers also tend to be more turbulent, however, and particles in the water increasingly attenuate light as depth increases.Seasonal and diurnal factors might also play a role in light availability because the angle of incidence, the angle at which light strikes water can lead to light lost from reflection. Known as Beer's Law, the shallower the angle, the more light is reflected and the amount of solar radiation received declines logarithmically with depth.Additional influences on light availability include cloud cover, altitude, and geographic position (Brown 1987).

Abiotic factors of Lotic Ecosystems.

http://en.wikipedia.org/wiki/Lotic_system_ecology

Flow
Water flow is the key factor in lotic systems influencing their ecology. The strength of water flow can vary between systems, ranging from torrential rapids to slow backwaters that almost seem like lentic systems. The speed of the water flow can also vary within a system and is subject to chaotic turbulence. This turbulence results in divergences of flow from the mean downslope flow vector as typified by eddy currents. The mean flow rate vector is based on variability of friction with the bottom or sides of the channel, sinuosity, obstructions, and the incline gradient.In addition, the amount of water input into the system from direct precipitation, snowmelt, and/or groundwater can affect flow rate. Flowing waters can alter the shape of the streambed through erosion and deposition, creating a variety of habitats, including riffles, glides[disambiguation needed], and pools.

Unifying characteristics of the ecology of running Waters.

http://en.wikipedia.org/wiki/Lotic_system_ecology

The following unifying characteristics make the ecology of running waters unique from that of other aquatic habitats.

• Flow is unidirectional.
• There is a state of continuous physical change.
• There is a high degree of spatial and temporal heterogeneity at all scales (microhabitats).
• Variability between lotic systems is quite high.
• The biota is specialized to live with flow conditions.

Lotic Ecosystems.

http://en.wikipedia.org/wiki/Lotic_system_ecology

River ecosystems are prime examples of lotic ecosystems. Lotic refers to flowing water, from the Latin lotus, washed. Lotic waters range from springs only a few centimeters wide to major rivers kilometers in width.Much of this article applies to lotic ecosystems in general, including related lotic systems such as streams and springs. Lotic ecosystems can be contrasted with lentic ecosystems, which involve relatively still terrestrial waters such as lakes and ponds. Together, these two fields form the more general study area of freshwater or aquatic ecology.

River Ecosystem.

http://en.wikipedia.org/wiki/Lotic_system_ecology

The ecosystem of a river is the river viewed as a system operating in its natural environment, and includes biotic(living) interactions amongst plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions.

Early work of Hydrobiologists.

http://en.wikipedia.org/wiki/Hydrobiology

Much of the early work of hydrobiologists concentrated on the biological processes utilised in sewage treatment and water purification especially slow sand filters. Other historically important work sought to provide biotic indices for classifying waters according to the biotic communities that they supported. This work continues to this day in Europe in the development of classification tools for assessing water bodies for the EU water framework directive.

Eutrophication.

http://en.wikipedia.org/wiki/Hydrobiology

One of the significant areas of current research is eutrophication. Special attention is paid to biotic interactions in plankton assemblage including the microbial loop, the mechanism of influencing water blooms, phosphorus load and lake turnover. Another subject of research is the acidification of mountain lakes. Long-term studies are carried out on changes in the ionic composition of the water of rivers, lakes and reservoirs in connection with acid rain and fertilisation. One goal of current research is elucidation of the basic environmental functions of the ecosystem in reservoirs, which are important for water quality management and water supply.

Hyrobiology.

http://en.wikipedia.org/wiki/Hydrobiology

Hydrobiology is the science of life and life processes in water. Much of modern hydrobiology can be viewed as a sub-discipline of ecology but the sphere of hydrobiology includes taxonomy, economic biology, industrial biology, morphology, physiology etc. The one distinguishing aspect is that all relate to aquatic organisms. Much work is closely related to limnology and can be divided into lotic system ecology (flowing waters) and lentic system ecology (still waters).

Mom ‘Trusting God’ for Ebola-Infected U.S. Doctor’s Life.

http://www.bloomberg.com/news/2014-07-28/mom-trusting-god-for-ebola-infected-u-s-doctor-s-life.html

Kent Brantly, a 33-year-old doctor who volunteered to fight deadly Ebola in Africa soon after finishing his hospital residency in Texas, is one of two U.S.citizens being treated for the disease.

“We’re just trusting God for his life,” the physician’s mother, Jan Brantly, said in a telephone interview from Indianapolis. “We’re praying, and we’re sustained by our faith.”

Ebola has killed 672 people in four West African nations since March, the worst outbreak since the virus was first reported in what is now the Democratic Republic of Congo in 1976. With no known cure, the illness can lead to bleeding from the eyes, ears and nose, and causes death in as many as 90 percent of those who get it.

More than 1,200 people have been infected, the World Health Organization said yesterday in astatement.

Brantly, the medical director of the Ebola center run by Samaritan’s Purse in Liberia’s capital of Monrovia, and Nancy Writebol, a worker at the center, are being treated there, the Boone, North Carolina-based charity said in a statement. They are each married with two children, the group said. The doctor’s family is in the U.S. while the whereabouts of Writebol’s family haven’t been released.

Brantly has been in Liberia since October 2013, according to his mother. “He was prepared to be a medical missionary. and that’s what he has chosen to do with his life,” Jan Brantly said yesterday. “He and his wife have always had that plan and that dream.”

The Ebola virus is transmitted from wild animals including chimpanzees, gorillas and bats, according to the Geneva-based WHO. Humans spread it through contact with bodily fluids. It causes fever, diarrhea and vomiting.

Nigeria reported its first case last week after an infected Liberian man landed in Lagos, Africa’s largest city. Liberia has shut all minor border crossings and is setting up testing centers at major entry points, AllAfrica.com reported, citing a government statement. The disease victim, Peter Sawyer, worked at Liberia’s finance ministry.

Liberia shut the ministry yesterday and said officials who had contact with Sawyer will be watched for signs of the illness. The ministry is scheduled to reopen today.

“As this epidemic goes on, this sort of thing is eventually probably going to happen,” said Ben Neuman, a virologist at the University of Reading in the U.K., speaking of how the outbreak may spread.

Stable Condition

Brantly is in stable condition, Strickland said, adding, “It’s easy to figure out what kind of person volunteers to take on this mission. He’s a highly skilled professional, he’s courageous, he’s compassionate.”

Brantly remains hopeful and steadfast in his faith, McRay said.

“He’s very hopeful and praying for his recovery but he’s also very knowledgeable about the course of his illness,” McRay said, after speaking yesterday with Brantly. Brantly has kept in communication with his wife, who left with their 3-year-old and 5-year-old children before Kent Brantly had symptoms, McRay said.

“She’s terrified, and yet hopeful and prayerful, shares her husband’s deep faith and deep resolve,” McRay said. “They have no doubts and no regrets about their decision.”

There is no cure or vaccine for Ebola, according to the U.S. Centers for Disease Control and Prevention. Treatment focuses on replenishing fluids, maintaining proper blood pressure and replacing lost blood, as well as treating any other infections.

Highest Risk

Medical staff are at the highest risk of contracting the virus because of their proximity to patients. Health workers attending to the patient should wear gloves, gowns and face visors to prevent contact between the patient’s bodily fluids and their own mucus membranes, such as the eyes, mouth, nose and ears, said Heymann, who has studied Ebola since 1976.

Strickland called Brantly “meticulous,” saying that’s why he was given the job in the first place. “We have every confidence that those protocols were not breached,” she said. The group is investigating how Brantly may have been exposed, according to Strickland.

Denial the disease exists, hostility to medical workers, a lack of medical supplies and below-standard hygiene are complicating efforts to contain the spread of the disease. In Sierra Leone, victims’ families have attacked doctors, while in neighboring Liberia the husband of a victim tried to burn the hospital down where his wife died.

In recent surveys by Samaritan’s Purse, 84 percent of 2,920 Monrovia residents surveyed said they didn’t believe Ebola was real, according to the group’s website.

Staff of the North Carolina-based charity Samaritan's Purse puts on protective gear at the ELWA hospital in the Liberian capital of Monrovia, on July 24, 2014.

Standard Methods for the Examination of Water and Wastewater.

http://en.wikipedia.org/wiki/Aquatic_toxicology

Standard Methods for the Examination of Water and Wastewater – A compilation of techniques for the examination of water, jointly published by the American Public Health Association (APHA), the American Water Works Association (AWWA), and the Water Pollution Control Federation (WPCF).

ASTM International.

http://en.wikipedia.org/wiki/Aquatic_toxicology

American Society for Testing and Materials (ASTM International) – A consensus organization, representing 135 countries, that develops and delivers international voluntary standard methods for aquatic toxicity testing.

Effects that occur when an organism is exposed to Toxicants.

http://en.wikipedia.org/wiki/Aquatic_toxicology

There are a number of effects that occur when an organism is simultaneous exposed to two or more toxicants. These effects include additive effects, synergistic effects, potentiation effects, and antagonistic effects. An additive effect occurs when combined effect is equal to a combination or sum of the individual effects. A synergistic effect occurs when the combination of effects is much greater than the two individual effects added together. Potentiation is an effect that occurs when an individual chemical has no effect is added to a toxicant and the combination has a greater effect than just the toxicant alone. Finally, an antagonistic effect occurs when a combination of chemicals has less of an effect than the sum of their individual effects.

Toxicological Effects.

http://en.wikipedia.org/wiki/Aquatic_toxicology

Toxicity can be broken down into two broad categories of direct and indirect toxicity. Direct toxicity results from a toxicant acting at the site of action in or on the organism. Indirect toxicity occurs with a change in the physical, chemical, or biological environment.

Lethality is most common effect used in toxicology and used as an endpoint for acute toxicity tests. While conducting chronic toxicity tests sublethal effects are endpoints that are looked at. These endpoints include behavioral, physiological, biochemical, histological changes.

Sediment Tests.

http://en.wikipedia.org/wiki/Aquatic_toxicology

At some point most chemicals originating from both anthropogenic and natural sources accumulate in sediment. For this reason, sediment toxicity can play a major role in the adverse biological effects seen in aquatic organisms, especially those inhabiting benthic habitats. A recommended approach for sediment testing is to apply the Sediment Quality Triad (SQT) which involves simultaneously examining sediment chemistry, toxicity, and field alterations so that more complete information can be gathered. Collection, handling, and storage of sediment can have an effect on bioavailability and for this reason standard methods have been developed to suit this purpose.

Effluent toxicity tests are tests conducted under the Clean Water Act.

http://en.wikipedia.org/wiki/Aquatic_toxicology

Effluent toxicity tests are tests conducted under the Clean Water Act, National Pollutant Discharge Elimination System (NPDES) permit program and are used by dischargers of contaminated effluent to monitor the quality of effluent into receiving waters. Acute Effluent Toxicity Tests are used to monitor the quality of industrial effluent monthly using acute toxicity tests. Effluent is used to perform static-acute multi concentration toxicity tests with C. dubia and P. promelas. The test organisms are exposed for 48 hours under static conditions with five concentrations of the effluent. Short-term Chronic Effluent Toxicity Tests are used to monitor the quality of municipal wastewater treatment plants effluent quarterly using short-term chronic toxicity tests. The goal of this test is to ensure that the wastewater is not chronically toxic. The major deviation in the short-term chronic effluent toxicity tests and the acute effluent toxicity tests is that the short-term chronic test lasts for seven days and the acute test lasts for 48 hours.

Freshwater tests and saltwater Tests.

http://en.wikipedia.org/wiki/Aquatic_toxicology

Freshwater tests and saltwater tests have different standard methods, especially as set by the regulatory agencies. However, these tests generally include a control (negative and/or positive), a geometric dilution series or other appropriate logarithmic dilution series, test chambers and equal numbers of replicates, and a test organism. Exact exposure time and test duration will depend on type of test (acute vs. chronic) and organism type. Temperature, water quality parameters and light will depend on regulator requirements and organism type.

Bioaccumulation Tests.

http://en.wikipedia.org/wiki/Aquatic_toxicology

Bioaccumulation tests are toxicity tests that can be used for hydrophobic chemicals that may accumulated in the fatty tissue of aquatic organisms. Toxicants with low solubilities in water generally can be stored in the fatty tissue due to the high lipid content in this tissue. The storage of these toxicants within the organism may lead to cumulative toxicity. Bioaccumulation tests use bioconcentration factors (BCF) to predict concentrations of hydrophobic contaminants in organisms. The BCF is the ratio of the average concentration of test chemical accumulated in the tissue of the test organism (under steady state conditions) to the average measured concentration in the water.

Short-term sublethal Tests.

http://en.wikipedia.org/wiki/Aquatic_toxicology

Short-term sublethal tests are used to evaluate the toxicity of effluents to aquatic organisms. These methods are developed by the EPA, and only focus on the most sensitive life stages. Endpoints for these test include changes in growth, reproduction and survival. NOECs, LOECs and EC50s are reported in these tests.

Critical life Stage Tests.

http://en.wikipedia.org/wiki/Aquatic_toxicology

Early life stage tests are considered as subchronic exposures that are less than a complete reproductive life cycle and include exposure during early, sensitive life stages of an organism. These exposures are also called critical life stage, ebryo-larval, or egg-fry tests. Early life stage tests are not considered valid if mortality in the control sample is greater than 30%.

Chronic Tests .

http://en.wikipedia.org/wiki/Aquatic_toxicology

Chronic tests are long-term tests (weeks, months years), relative to the test organism’s life span (>10% of life span), and generally use sub-lethal endpoints. In chronic exposures, organisms come into contact with low, continuous doses of a toxicant. Chronic exposures may induce effects to acute exposure, but can also result in effects that develop slowly. Chronic tests are generally considered full life cycle tests and cover an entire generation time or reproductive life cycle (“egg to egg”). Chronic tests are not considered valid if mortality in the control sample is greater than 20%. These results are generally reported in NOECs (No observed effects level) and LOECs (Lowest observed effects level).

There are various types of tests:- Acute Tests.

http://en.wikipedia.org/wiki/Aquatic_toxicology

Acute tests are short-term exposure tests (hours or days) and generally use lethality as an endpoint. In acute exposures, organisms come into contact with higher doses of the toxicant in a single event or in multiple events over a short period of time and usually produce immediate effects, depending on absorption time of the toxicant. These tests are generally conducted on organisms during a specific time period of the organism’s life cycle, and are considered partial life cycle tests. Acute tests are not valid if mortality in the control sample is greater than 10%. Results are reported in EC50, or concentration that will affect fifty percent of the sample size.

Flow-through Test.

http://en.wikipedia.org/wiki/Aquatic_toxicology

Flow-through- a flow through test exposes the organism to the toxicant with a flow into the test chambers and then out of the test chambers. The once-through flow can either be intermittent or continuous. A stock solution of the correct concentrations of contaminant must be previously prepared. Metering pumps or diluters will control the flow and the volume of the test solution, and the proper proportions of water and contaminant will be mixed.

Renewal Test.

http://en.wikipedia.org/wiki/Aquatic_toxicology

Renewal- a renewal test also exposes the organism to the toxicant in a similar manner as the static test because it is in still water. However, in a renewal test the test solution is renewed periodically (constant intervals) by transferring the organism to a fresh test chamber with the same concentration of toxicant.

Recirculation type of Exposure System.

http://en.wikipedia.org/wiki/Aquatic_toxicology

Recirculation- a recirculation test exposes the organism to the toxicant in a similar manner as the static test, except that the test solutions are pumped through an apparatus (i.e. filter) to maintain water quality, but not reduce the concentration of the toxicant in the water. The water is circulated through the test chamber continuously, similar to an aerated fish tank. This type of test is expensive and it is unclear whether or not the filter or aerator has an effect on the toxicant.