The last 30 days have been extremely volatile for the S&P/ASX 200 (Index: ^AXJO) (ASX: XJO). Having started the period at 5,519 points, the benchmark index was as low as 5,200 points at one stage. It has now managed to claw its way back to 5,421 points, reducing its monthly decline to 1.7% in the process.

Unfortunately this drop is nothing compared to the shocking drops that shareholders of these four shares have had to endure in the last 30 days. Here’s why they plummeted:

Estia Health Ltd (ASX: EHE)

The embattled aged care provider’s share price has plunged by around 29% in the last 30 days over concerns that it will be impacted by an update on guidelines for additional private fees in residential aged care from the federal government. According to The Australian analysts at Macquarie Group Ltd (ASX: MQG) have estimated these reforms equate to a $20 per resident, per day, hit to revenue for aged care operators.

Galaxy Resources Limited (ASX: GXY)

This lithium producer’s shares are down almost 21% in the last month possibly down to investors being concerned that the lithium boom could be heading for a bust. Whilst demand for lithium-ion to be used in the batteries of smartphones and electric cars is on the rise, so too is the number of miners entering the space. The more companies that start producing lithium, the more pressure there will be on lithium prices.

OFX Group Ltd (ASX: OFX)

The shares of this provider of international payments and foreign exchange services have dropped almost 25% in the last month, with the majority of these declines coming in the last week. Although there was no news out of the company, I believe the lack of volatility in currency markets may be the reason for the decline. When currency markets are volatile like they were during the Brexit, OFX’s services experience strong demand. But with these markets remaining relatively stable recently, I’m sure investors are concerned that the company will be struggling to grow as strongly as it has previously forecast.

TPG Telecom Ltd (ASX: TPM)

The telco giant has lost over a quarter of its market value in the last 30 days. The 27% decline in its share price came after it revealed higher capital expenditures and lower-than-expected growth forecasts for the year ahead. I feel confident that the NBN rollout is an opportunity for TPG Telecom to gain market share and believe this sell off is a great opportunity for investors to pick up shares at a great entry price for a long-term investment.

If your portfolio has taken a hit in the last month don't worry. These fast-growing shares could be just what your portfolio needs to take it higher in the next few months if you ask me.

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Motley Fool contributor James Mickleboro has no position in any stocks mentioned. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.