Biogeochemistry Book Review Coastal Management Human Health Human impacts Pollution

From Wastewater to Seahorses to the Medicine Cabinet

Zhang, Wei, et al. “Bioaccumulation of Metals in Tissues of Seahorses Collected from Coastal China.” Bulletin of environmental contamination and toxicology 96.3 (2016): 281-288.


Pollution along coastal waterways can have negative impacts on the environment that may put human health at risk. For example, scientists fear that marine pollutants, like metals, will be a residual in a medicine derived from seahorse tissue, and they are concerned for the potential harm it may have on patients.

Metal pollution is most prevalent in areas that have a lot of people, and a lot of growth and expansion.   These types of communities create a lot of waste products through civilians, like sewage and automobile exhaust, and industry, like mining, electronic waste recycling, and smelting (the process of extracting metal from it’s ore source). Metals are transported from coastal areas to the marine system by wastewater, runoff, and wind. Wind is a big factor in the distribution of automobile exhaust, which contributes to the pollution of cadmium (Cd) and lead (Pb).

Once in the water column, the metals either are consumed or settle out. Eventually, they can work their way into and up the food chain, and accumulate in the tissues of consumers, like seahorses.

Figure 1: H. trimaculatus (source:,_Osezaki.jpg)
Figure 1: H. trimaculatus (source:,_Osezaki.jpg)

Seahorses (figure 1) are neat little sea creatures. Their use in medicine and unique appearance make them a popular catch. They live near the bottom of shallow (10’s meters) and warm bays and estuaries in mid to low latitudes.   They are often found in areas of seagrass, mangroves, and coral reefs. Seahorses are carnivorous, however, they have relatively small appetites and their digestive system is not very good at reaping the benefits of what they do consume. Nonetheless, they are still living in environments impacted by pollution so the possibility of metal contamination in their tissues that would translate into human medicine is a real threat.


An early step in studying the threats to human health from metals in seahorse tissues used to make medicine is to determine if the metal pollutants are accumulating in seahorses’ tissues.   Scientists sampled specimen from six locations along the coast of China so that their study would represent both developed and under developed regions. The sampling locations included Qingdao (figure 2), Zhoushan, Xiamen, Shanwei, Zhanjiang, and Beihai. Sampling was completed during October and November in 2010 with the aid of local fishing vessels.   A total of four different species of seahorses were caught: Hippocampus trimaculatus, Hippocampus histrix, Hippocampus kelloggi, and Hippocampus kuda.  H. trimaculatus were caught in every location except for Shanwei, where H. kuda was caught instead. At Xiamen and Zhanjiang, H. histrix and H. kelloggi were caught in addition to H. trimaculatus, respectively.

City of Qingdao (source:
City of Qingdao (source:

Specimens brought back to the laboratory were dissected. The tissues were then dried, powered, and digested for further analysis. Concentrations of metals (aluminum, barium, cadmium, cesium, chromium, copper, magnesium, manganese, and lead) were measured on an ICP-MS (inductively coupled plasma mass spectrometer). Figure 1 in the original article maps the locations for sampling, the types of seahorses sampled, and the metal concentrations of the seahorses sampled.


Overall the metal with the greatest concentrations in seahorse tissue was magnesium, followed by aluminum and manganese.   Figure 2 in the original article illustrates the results for each element in each species in bar graphs.

Scientists found that the metal concentrations varied by sample location, species, and tissue type.

The variation in metal accumulation with respect to location was investigated with H. trimaculatus because it had a large distribution range. Researchers speculate that the concentration differences between locations may reflect industrial activity and civilian land use resulting in the discharge of metal-containing wastewater into the coastal waters.   For instance, the high levels of metals measured in the tissues of seahorses from Qingdao and Xiamen are likely attributed to those areas both having experienced fast economic development. In comparison, areas like Zhoushan and Beihai are popular tourist destinations and as a result have much less industrial wastewater discharging into and polluting the coastal waterways.

Accumulation differences found between the different types of species were observed and may be related to appetite differences between species.   For example, H. kelloggi had greater amounts of metal accumulation than H. trimaculatus and scientists think the elevated metal concentrations observed in H. kelloggi may be explained by the diet a heavy in benthic prey. Benthic organisms are susceptible to metal contamination because of their location at the bottom of the water column where all the sediments and pollutants settle out.   Additional explanations for the variation in metal concentrations observed between species include differences in kinetic properties of the metals, and differences in physiological functionality between species.

Scientists also found that metal concentration varied with tissue type. Greater levels of metal were measured in muscle and skin tissues and lesser amounts were measured in the brain, gill, and skeletal tissues. The tissue variation was different between species and was very irregular; the results are summarized in table 2 of the original article.

Compared with marine fish in the same areas, the seahorses had lesser amounts of cadmium, chromium, manganese, and lead, but a greater concentration of copper.   The metals with lower concentrations can be explained by the low consumption rate by the seahorses; because the seahorses do not eat much, they are not susceptible to accumulating a lot of metal in their tissues. The copper, however, is less straightforward. Researchers find the high concentration of copper in seahorse tissue relative to marine fish quizzical because they did not find that the seahorses up took the copper quickly nor did they find the copper in forms readily available for uptake. Why copper is able to accumulate in the tissues of seahorses is a topic for further investigation.

Scientists on this paper took a first step to assessing the threat of metal pollutants on human health with respect to their residual imprint in medicines derived from seahorse tissues.   They found that seahorses do accumulate metal in their tissues, but not as much as fish do, and there is a lot of variability between location, species, and tissue type.   Their research is important for human health, but also to understand how pollution is impacting the health of the marine system.   Responsible waste management can be an advantage in conserving seahorse populations, which are low enough to have the seahorse listed on the endangered species list by the Convention on International Trade in Endangered Species of Wild Fauna and Flora.

2 thoughts on “From Wastewater to Seahorses to the Medicine Cabinet

  1. Article: From Wastewater to Seahorse to the Medicine Cabinet  Author: Anne M. Hartwell
    Pollution has many negative effects on the environment. Metal pollutants that drain into the oceans are eaten by seahorses. These metals end up in the seahorses’ tissues. Many medicines are made by these tissues and patients who consume these medicines put their health at risk. To see if the metal accumulated inside the seahorse tissues, scientists sampled six different specimens located near the coast of China and dissected them. The tissues were dried, powered, and digested sfor further analysis. They found that metal concentration depended on the location, seahorse species, and the tissue type. They also found that the seahorse tissue mostly contained  magnesium and alluminum. Metal concentrain also depends on what a species eats. For example, if one species’ diet consisted of plankton that contained metal in its tissues , then it would have a higher metal concentration than a species that ate plankton without metal in its tissues. It is important to manage our waste so that we do not affect other animals and so we do not risk peoples’ health.
    Question- Are there any other methods, besides managing our waste, to make sure metal does not affect marine animals? Is it possible to check medicine if it contains metals so we do not harm our health?

    1. Hey Drishti!

      Welcome to and thank you for commenting.

      Managing waste that eventually is transported into the ocean is a huge umbrella. Metals can from waste, like trash, but it can also come from emission and it can be leached from materials that we bury for infrastructure, for examples. On a regional, national, and international scale it is important that agencies oversee activities to try an limit the metals that are released into the environment. Like we learned in the article, when metals accumulate in an animals tissue it can have long term health impact, so the less we add to the environment from various sources, the better. Metals do exist in the natural environment (think about the metals listed on the periodic table- like iron or lead!), so we’ll always expect that some will be detected.
      As for checking if your medicine contains metals, I imagine that you could reference the label on the bottle. You could also ask your pharmacist, or find an accredited internet resource. And just like in natural enviornment, there is some metal that is naturally occurring in our bodies. For example our blood has a level of iron, and if it’s too low you can’t donate blood! Usually a nice healthy serving of spinach can help get the lead levels back up though!

      Thanks for reading my post, i hope this helps answer your questions!


Leave a Reply

Your email address will not be published.