Which chemical poses the greatest risk in rivers? UK risk ranking.

Transcription from Professor Andrew Johnson's presentation Society of Environmental Toxicology and Chemistry (SETAC) Europe 26th Annual Meeting

In this talk I'd like to review a project that we've done recently on trying to identify the single most dangerous chemical present in British rivers following a risk ranking exercise.
I've often thought throughout my career whether the chemical I was working on was actually the one of greatest concern to wildlife. 

This project was attempted to set up a system that could review this in a rational way.

Slide 2 Why should we begin risk ranking chemicals? 

Well, what we want to avoid, for one thing, is the push and pull of fashions driving us in different directions whether it be nano particle anti-androgens, neonicotinoids which may be irrelevant to what the major problem is with chemicals in the environment.

Slide 3 Why should we begin risk ranking chemicals?

Essentially what we are doing is setting up a framework that might persuade funders to focus their support on chemicals which are of the greatest risk and causing the greatest problems to wildlife.

Slide 4 We compared these chemical groups against each other

So what have we did was to pull together dissimilar groups of chemicals that are known to be in our rivers. These included metals, pesticides, pharmaceuticals, persistent organic pollutants (POPs), nano-particles, surfactants and others. We picked 10 or more from the different groups. These individual chemicals where not selected at random. We tried to identify chemicals that are prominent in the literature and considered by the community to be a significant concern for the freshwater environment.

Slide 5 Risk ranking method

This analysis is really a literature review. We collect effect data using a search in literature with keywords; we are looking for European and UK species and a range of endpoints.  
It is largely an uncritical process and one paper can only provide one data point for one species such as an EC50. We are looking for around 50 to 100 records per chemical and we want include algae plants, invertebrates and fish at the very least.

Regarding quality we are wanting to hold on to only where the ecotox study used measured concentrations. Although for pharmaceuticals because there's not much literature we took everything that was present on those chemicals, uncritically. 

We compared this against observed river measurements either collected by our regulator in the UK or the scientific literature. Where we had very little river measurement we might use European water data or we might use predicted river concentrations for Britain's Rivers based on regional dilution values and for low flows in particularly high impacted rivers. 

What we are comparing is all the effects data (see figure on the right), each point is the single item of information, on one species for example, against the measured river data over the red data and we are comparing the medians - the two black circles - as the way to rank chemical.

Slide 7 Our chemicals risk ranking exercise was not

To reiterate what the chemical risk ranking exercise was not.
It was not traditional risk assessment, that's a different aim and it tends to start from a precautionary standpoint using LOECs and PNEC. We are not doing that. In fact, we want to stay away from giving too much weight to the data which appears to be showing effects at very low concentrations and some of that data may not be repeatable. We are trying avoiding using PECs, we are trying to use as much measured river data as possible and we are using the median.  We are not restricted to only OECD test species, we want a wide range as possible and a wide range of endpoints. We are not looking at micro-organisms. 

Slide 8 Results from comparing all the chemicals data

So, at the end of all this exhaustive process, this figure shows all of the data points collected. This is pairs data you are looking, with the ecotox data on the left hand side - of any pair - with reported river measurements on the right. So chemicals towards our left here are the highest risk because there median points - those two circles are closest together - and towards the right are the lowest risk as their medium to have very far apart.

Slide 9 Conversion of data into a risk ratio

Now what we can do is to simplify things by just using the ratio, or quotient, of the median river concentration divided by the median effect concentration. If you get a value of one that is obviously a disaster as that is obviously very high risk. So this is all the data now simply used as a ratio and we are seeing the metals on the high risk end, on the left of the log scale.  So we're looking at a difference of almost six fold in risk.

Slide 10 Where do metals come in the ranking?

So starting with the metals and remember this is a comparison of the median river and effect concentrations we see metals like aluminum, copper, zinc and manganese are a top risk. 
Meanwhile the two sample nano-particles, nano-zinc oxide and nano-silver are at the lower risk end - about 1000 fold lower risk than dissolved metals.

Slide 11 Where do pharmaceuticals come in the ranking?

With the pharmaceuticals we found most of them at the low risk and including diclofenac, but with one very distinct contradiction, ethinyl estradiol, which is the contraceptive pill. This stands out as a high risk for us.

Slide 12 Where do pesticides come from in the risk ranking?

Of the pesticides they span the whole range from high to low risk. Glyphosate, metaldehyde and neonicotinoids as examples appear to be low risk, while insecticides like chlorpyifos and methomyl are at the high risk end for our rivers.

Slide 13 Where do Persistent Organic Pollutants (POPs) come from in the risk ranking?

With the POPs it is a little bit difficult to use them in this analysis because exposure in the real world would likely be through diet and sediments. However ecotox data still relies on water exposure, so in our case here we lead on benzo[a]pyrine and Lindane, which is in fact an insecticide is our highest risk POPS and much higher concern some of the other POPS for wildlife. 

Slide 14 Where do surfactants come from in the risk ranking?

Moving onto the surfactants and others. A little bit to our surprise surfactants such as LAS come out as high risk as does alkyl ethoxysulphate and triclosan - the antimicrobial - while compounds such as bisphenol-A and DEHP are much lower risk.

Slide 15 Sub-lethal (chronic), ecotox effects using refined water data

Now we can use this data in a more refined way. In this case were only looking at sub lethal chronic ecotox effects and we are only using refined water data, so it is only neutral pH toxicity data, only dissolved concentrations, only UK reports and only reports from rivers from 2010 onwards.

Metals are towards the high risk and the left of the graph, led now by zinc but with LAS coming second and ethinyl estradiol coming very high up for risk.  So for example, looking at the, remembering it is a log scale, copper is 100,000 times greater risk to wildlife and rivers it would appear than the drug Naproxen.

Slide 16 Top 10 UK high risk chemicals 

We can use a variety of different approaches, which are listed here, giving the top 10 in order.
When we use the simple risk ranking, aluminum and copper come top. When we refine this, aluminum comes down because we are only interested in neutral pH. 
You can see with the lethal and sub lethal effects zinc still comes top with copper very close to it. Alkylbenzene sulphonate (LAS) is also in the top three and when looking at some lethal effects ethinyl estradiol comes into the top five.
If we are only interested in chemicals with of a bio-concentration factor higher than 500, as you can see on the right these two columns, metals stay top but we now get more insecticides in the top the list.

Slide 17 Which chemicals are regulated or not?

Another way of looking at the research is to review which chemicals in our group are regulated or not regulated. Most are regulated, as I mentioned earlier there are concerns around many of these chemicals, but the surfactants where we found a high risk are not regulated.

Slide 18 Messages from our rational risk ranking of chemicals 

-    Metals come out on top of our analysis led by zinc followed by copper, manganese, nickel, iron and cadmium for UK rivers.

-    The surfactant linear alkylbenzene sulphonate (LAS) comes high in our ranking even though it is considered to have little or no interest for the environment by most parties.

-    Another way of looking at the output from this research is we could say that the top 10 chemicals of concern will be a suitable selection for carrying out relevant mixture studies.

-    A rational risk ranking as we have done would not prioritise most pharmaceuticals or nano particles as being of significant concern with the exception of ethinyl estradiol and some of the highest ranked chemicals such as alkylbenzene sulphonate (LAS) are not currently regulated although others have no risk are.

You notice I have listed a couple of papers there which we publish that give you more detail on of this making process 

Slide 19 Final thoughts 

Is rational to spend the majority of our research funds on chemicals which might be only less than one per cent of the relative risk?

Related links

Staff page of Professor Andrew Johnson

SETAC Nantes 2016 conference website


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